X∼B(n,p), cumulative probabilities, mean & variance
Normal Distribution
X∼N(μ,σ2), standardisation, inverse normal
AS Level Mathematics is the first year of the A Level, offered by boards such as Cambridge (9709) and Edexcel. It blends Pure Mathematics with an introduction to Statistics and Mechanics.
What it covers
The Pure core runs through indices and surds, quadratics, coordinate geometry, graphs and transformations, trigonometry, and the first ideas of differentiation and integration. Applied units add probability, data handling and kinematics.
Pure
algebra · geometry · calculus
Statistics
data · probability
Mechanics
kinematics · forces
Calculator
allowed (most papers)
▲ How to use this course
Each chapter pairs a reference panel with worked examples; the explorers make slope, transformations and the gradient idea visual. Finish with the 50-problem set, then export it as a worksheet.
⚠ Cambridge 9709 Exam Rules & Accuracy Guidelines
Accuracy standard: Non-exact answers must be given to 3 significant figures, or 1 decimal place for angles in degrees, unless specified otherwise in the question. Do not round prematurely in intermediate steps.
Command words:'Show that' demands complete algebraic working with no skipped steps. 'Hence' means you must use the preceding result — alternate methods receive no credit.
Angle modes: Circular measure and calculus strictly require radian mode. Working in degrees for arc length or calculus formulas voids the entire solution.
Cambridge AS Level Mathematics 9709 Paper Marks: Pure Mathematics 1 (75 marks, 60% of AS) paired with Mechanics (50 marks, 40%) or Probability & Statistics (50 marks, 40%).
A student computes the volume of a cylinder using r=3.2 cm and h=7.85 cm. The raw calculator display shows 252.518.... How should the final answer be reported according to Cambridge AS Level guidelines?
Unless otherwise specified, non-exact numerical answers must be given to 3 significant figures. Rounding 252.518... to 3 s.f. gives 253 cm3. Giving 1 or 2 s.f., or excessive decimal places without justification, incurs an accuracy penalty (A1).
📝 Chapter Quiz
1
Indices, Surds & Quadratics
📌 Algebra — Indices, Surds & QuadraticsP1 · Laws of indices · Surds · Completing the square · Discriminant & nature of roots
The laws of indices, simplifying and rationalising surds, and the full toolkit for quadratics — factorising, completing the square and the formula.
▲ Reference — Algebra core
aman=am+n, a−n=an1, a1/n=na. Quadratic formula x=2a−b±b2−4ac; the discriminant b2−4ac fixes the number of real roots.
Indices
aman=am+n
Surds
ab=ab
Completing square
(x+2b)2−4b2
Discriminant
b2−4ac
Parabola y=2x2−5x−3 intersecting the x-axis at x=−21 and x=3, with vertex at (1.25,−6.125).
⚠ Common Traps & Exam Pitfalls
Completing the square when a=1: Factor a from the quadratic and linear terms before halving the coefficient: ax2+bx+c=a[x2+abx]+c=a(x+2ab)2−a(2ab)2+c. Forgetting to multiply the subtracted square by a is the most frequent algebraic slip.
Discriminant phrasing:'Real roots' means b2−4ac≥0 (includes repeated roots). 'Two distinct real roots' strictly requires b2−4ac>0. 'No real roots' means b2−4ac<0. If the leading coefficient contains a parameter k, remember k=0 for the equation to be quadratic.
Surd conjugates: To rationalise b+ca, multiply numerator and denominator by b−c. Expanding (b+c)(b−c)=b2−c eliminates the radical completely.
Worked example 1.A
Simplify 12.
4⋅3=23.
Worked example 1.B
Complete the square for x2+4x.
(x+2)2−4.
Solve the quadratic equation 2x2−5x−3=0 by completing the square. State the vertex of the corresponding parabola y=2x2−5x−3.
Factor 2 from the first two terms: 2(x2−25x)−3=0. Halve the coefficient of x: 21(−25)=−45. Complete the square: 2(x−45)2−2(1625)−3=0⇒2(x−45)2−825−824=0⇒2(x−45)2=849. Divide by 2: (x−45)2=1649. Take square roots: x−45=±47⇒x=45+7=3 or x=45−7=−21. The vertex is (45,−849)=(1.25,−6.125).
Express 2−53+5 in the form p+q5, where p and q are rational numbers to be found.
Multiply numerator and denominator by the conjugate of the denominator, 2+5: 2−53+5×2+52+5=22−(5)2(3+5)(2+5) Expanding the numerator: 3(2)+35+25+(5)2=6+55+5=11+55. The denominator is 4−5=−1. Therefore: −111+55=−11−55 Thus p=−11 and q=−5.
Find the set of values of the constant k for which the equation kx2+4x+(k−3)=0 has real roots.
For real roots, the discriminant Δ=b2−4ac≥0. Here a=k, b=4, c=k−3: Δ=42−4(k)(k−3)=16−4k2+12k≥0 Divide the entire inequality by −4, reversing the inequality sign: k2−3k−4≤0 Factor the quadratic: (k−4)(k+1)≤0. The critical values are k=−1 and k=4. Since the parabola opens upward, the product is ≤0 between the roots: −1≤k≤4. Note that if k=0, the equation becomes the linear equation 4x−3=0, which has one real root x=43, so k=0 is included. Thus, the solution set is −1≤k≤4.
📝 Chapter Quiz
2
Simultaneous Equations & Inequalities
📌 Simultaneous Equations & InequalitiesP1 · Linear & non-linear systems · Quadratic inequalities · Modulus function
Solving linear and linear-with-quadratic systems, and linear and quadratic inequalities.
▲ Reference — Systems & inequalities
Solve a linear system by substitution or elimination; for a linear–quadratic pair, substitute the linear equation into the quadratic. A quadratic inequality is solved by finding the roots and testing the sign of each interval.
Linear system
substitute / eliminate
Linear–quadratic
substitute the line
Sign rule
flip ≤ when ÷(−)
Quadratic ineq.
roots then test
Parabola y=x2−3 and line y=2x+1 intersecting at x=1±5.
⚠ Common Traps & Exam Pitfalls
Quadratic inequalities format: Never write x2>9⇒x>±3. Always find critical roots and sketch the parabola. For ax2+bx+c>0 (with a>0), the solution consists of two separate inequalities connected by 'or': x<r1 or x>r2. Combining them into r1>x>r2 loses the final mark.
Pairing coordinates in systems: After finding two values of x, substitute each into the linear equation to find the corresponding y. Pair them explicitly as (x1,y1) and (x2,y2). Substituting into the quadratic equation often creates false phantom pairings.
Modulus validity check: In equations like ∣ax+b∣=cx+d, any candidate solution that makes cx+d<0 is extraneous and must be discarded because absolute values are non-negative.
Worked example 2.A
Solve x+y=5, x−y=1.
Add: 2x=6:
x=3,y=2.
Worked example 2.B
Solve x2−4<0.
Roots ±2, curve below axis between them:
−2<x<2.
Solve the simultaneous equations: 2x+y=7x2+xy=12
From the linear equation, express y in terms of x: y=7−2x. Substitute into the second equation: x2+x(7−2x)=12⇒x2+7x−2x2=12⇒−x2+7x−12=0 Multiply by −1: x2−7x+12=0. Factor: (x−3)(x−4)=0, giving x=3 or x=4. For x=3: y=7−2(3)=1. For x=4: y=7−2(4)=−1. The solutions are (3,1) and (4,−1).
Find the set of values of x satisfying the inequality 2x2−7x+3≤0.
Find the critical values where 2x2−7x+3=0. Factor the quadratic: (2x−1)(x−3)=0, so the roots are x=21 and x=3. Since the coefficient of x2 is positive (a=2>0), the parabola opens upward. The quadratic is less than or equal to zero between and including the roots. Therefore, the solution set is 21≤x≤3.
Solve the inequality ∣3x−5∣<2∣x+1∣.
Both sides are non-negative, so we can square both sides: ∣3x−5∣2<4∣x+1∣2⇒9x2−30x+25<4(x2+2x+1) Expand and simplify: 9x2−30x+25<4x2+8x+4⇒5x2−38x+21<0 Factor: (5x−3)(x−7)<0. The critical values are x=53 and x=7. Since the parabola opens upward, the expression is strictly negative between the roots: 53<x<7.
Sketching standard curves and applying translations, reflections and stretches.
▲ Reference — Transformations of y=f(x)
f(x)+a shifts up by a; f(x−a) shifts right by a; −f(x) reflects in the x-axis; af(x) stretches vertically by factor a.
The grey curve is y=sinx; the indigo curve is y=sin(x−h)+k. Slide h and k to translate it.
⊙ Explorer · Translating a graphinteractive
sin(x) vs. the translated curve
x
sin(x)
translated
translation (h, k)—
Inside the function, x−h moves right; outside, +k moves up.
Up by a
f(x)+a
Right by a
f(x−a)
Reflect (x-axis)
−f(x)
Stretch
af(x)
Transformation of y=x2 to y=2(x−2)2−3: translated by (2−3) and stretched vertically by scale factor 2.
⚠ Common Traps & Exam Pitfalls
Horizontal vs vertical operations: Operations inside the argument f(…) affect x inversely: f(x−a) translates right by +a, and f(kx) stretches horizontally by scale factor k1. Operations outside affect y directly: af(x) stretches vertically by a, and f(x)+c shifts up by c.
Order of horizontal transformations: For f(ax+b), always factor the bracket: f(a(x+ab)). This represents a horizontal stretch by scale factor a1 followed by a translation by vector (−ab0), OR a translation of −b followed by stretch of a1. Stating transformations in the wrong order loses all marks.
Reflection axes:y=−f(x) is a reflection in the x-axis (y→−y). y=f(−x) is a reflection in the y-axis (x→−x).
Worked example 3.A
Describe y=(x−2)2 relative to y=x2.
It is a translation 2 units to the right.
Worked example 3.B
Describe y=−x2 relative to y=x2.
A reflection in the x-axis.
The curve y=f(x) has a stationary point at (4,−6). State the coordinates of the corresponding stationary point on the curve: (a) y=f(x+3)+2, (b) y=3f(2x), (c) y=−f(−x).
(a) y=f(x+3)+2 translates 3 units left and 2 units up: (4−3,−6+2)=(1,−4). (b) y=3f(2x) stretches horizontally by 21 and vertically by 3: (4×21,−6×3)=(2,−18). (c) y=−f(−x) reflects in both axes (point reflection through the origin): (−4,−(−6))=(−4,6).
The curve y=x2−6x+5 can be mapped to y=x2 by a sequence of two geometric transformations. Express the equation in vertex form, state the vertex, and describe fully each transformation.
Complete the square: y=(x−3)2−9+5=(x−3)2−4. The vertex of the parabola is (3,−4). To map y=(x−3)2−4 back to y=x2, we must translate the graph 3 units to the left and 4 units upwards. In vector notation, this is a single translation by (−34), or two sequential transformations: (1) Translation by vector (−30) (3 units left), and (2) Translation by vector (04) (4 units up).
📝 Chapter Quiz
4
Coordinate Geometry
📌 Coordinate GeometryP1 · Line equations · Circle equation & properties · Tangent to a circle
Straight lines — gradient, midpoint, distance and equations — and the equation of a circle.
▲ Reference — Lines & circles
Gradient m=x2−x1y2−y1; line y−y1=m(x−x1). A circle with centre (a,b) and radius r is (x−a)2+(y−b)2=r2.
Adjust gradient m and intercept b of y=mx+b; the amber dots are the intercepts.
⊙ Explorer · Gradient & interceptsinteractive
Sampled points along the current line
x
y
gradient—
y-intercept—
x-intercept—
Perpendicular gradients satisfy m1m2=−1.
Gradient
x2−x1y2−y1
Line
y−y1=m(x−x1)
Distance
Δx2+Δy2
Circle
(x−a)2+(y−b)2=r2
Circle with centre (3,−1) and radius r=5, passing through P(7,2) with equation (x−3)2+(y+1)2=25.
⚠ Common Traps & Exam Pitfalls
Circle center signs: The equation is (x−a)2+(y−b)2=r2. In (x−3)2+(y+1)2=25, the center is (+3,−1), NOT (−3,1). Also, the right-hand side is r2, so the radius is 25=5, not 25.
Perpendicular lines: Gradients satisfy m1m2=−1, giving m⊥=−m1. A frequent error is forgetting the negative sign (reciprocal without negation).
Circle geometry properties: (1) The tangent to a circle is perpendicular to the radius at the point of contact. (2) The perpendicular bisector of any chord passes through the center of the circle. (3) The angle in a semicircle is a right angle.
Worked example 4.A
Find the gradient through (1,2) and (4,11).
4−111−2=3.
Worked example 4.B
State the centre of (x−2)2+(y+3)2=25.
(2,−3).
Find the equation of the perpendicular bisector of the line segment joining A(−2,5) and B(4,−3). Give your answer in the form ax+by+c=0, where a,b,c are integers.
1. Midpoint of AB: M=(2−2+4,25−3)=(1,1). 2. Gradient of AB: mAB=4−(−2)−3−5=6−8=−34. 3. Gradient of perpendicular bisector: m⊥=−−4/31=43. 4. Equation of line passing through M(1,1): y−1=43(x−1)⇒4(y−1)=3(x−1)⇒4y−4=3x−3 Rearrange to standard integer form: 3x−4y+1=0.
The circle C has equation x2+y2−6x+4y−12=0. (a) Find the coordinates of the centre and the exact radius of C. (b) Find the equation of the tangent to C at the point P(6,2).
(a) Complete the squares for x and y: (x2−6x+9)+(y2+4y+4)=12+9+4⇒(x−3)2+(y+2)2=25 The centre is (3,−2) and the radius is 25=5. (b) The gradient of the radius from centre (3,−2) to P(6,2) is: mrad=6−32−(−2)=34 The tangent is perpendicular to the radius, so its gradient is mtan=−43. Using point-slope form with P(6,2): y−2=−43(x−6)⇒4(y−2)=−3(x−6)⇒4y−8=−3x+18⇒3x+4y−26=0 In slope-intercept form: y=−43x+213.
📝 Chapter Quiz
5
Trigonometry
📌 TrigonometryP1 · Exact trig values · sin2θ+cos2θ=1 · Solving trig equations in a range
Exact values, the identity linking sine and cosine, and solving simple trigonometric equations.
▲ Reference — Trig essentials
sin2θ+cos2θ=1 and tanθ=cosθsinθ. Exact values: sin30∘=21, cos30∘=23, sin60∘=23. The sine and cosine curves have period 360∘.
Identity
sin2θ+cos2θ=1
Tangent
cosθsinθ
Exact
sin60∘=23
Period
360∘
Unit circle showing angle 210∘ in Quadrant III with reference angle 30∘ and coordinates (−23,−21).
⚠ Common Traps & Exam Pitfalls
Never divide by trig terms: In equations such as 2sinθcosθ=sinθ, dividing by sinθ destroys the roots where sinθ=0. Always rearrange to one side and factor: sinθ(2cosθ−1)=0.
Compound angle domain: When solving an equation like cos(2x−30∘)=21 for 0∘≤x≤180∘, first transform the domain for u=2x−30∘: −30∘≤u≤330∘. Find all valid values for u within this adjusted window, then solve for x.
Identity substitution: Always check if replacing sin2θ with 1−cos2θ (or vice-versa) creates a single-variable quadratic in cosθ or sinθ.
Worked example 5.A
Solve sinθ=21 for 0∘≤θ≤180∘.
θ=30∘,150∘.
Worked example 5.B
State the exact value of sin60∘.
23.
Solve the equation 2cos2θ−sinθ−1=0 for 0∘≤θ≤360∘.
Use the Pythagorean identity cos2θ=1−sin2θ: 2(1−sin2θ)−sinθ−1=0⇒2−2sin2θ−sinθ−1=0⇒−2sin2θ−sinθ+1=0 Multiply by −1: 2sin2θ+sinθ−1=0. Factor: (2sinθ−1)(sinθ+1)=0. 1. 2sinθ−1=0⇒sinθ=21. In [0∘,360∘], θ=30∘ or 180∘−30∘=150∘. 2. sinθ+1=0⇒sinθ=−1. In [0∘,360∘], θ=270∘. The complete solution set is θ=30∘,150∘,270∘.
Prove the identity: 1−sinθcosθ−1+sinθcosθ≡2tanθ
Start with the left-hand side and write over a common denominator: LHS=(1−sinθ)(1+sinθ)cosθ(1+sinθ)−cosθ(1−sinθ) Expand the numerator: cosθ+cosθsinθ−cosθ+cosθsinθ=2cosθsinθ. Expand the denominator: 1−sin2θ=cos2θ. Substitute both back: LHS=cos2θ2cosθsinθ=cosθ2sinθ=2tanθ=RHS Q.E.D.
Solve the equation tan(2x−20∘)=3 for 0∘≤x≤180∘.
Let u=2x−20∘. As 0∘≤x≤180∘, the domain for u is −20∘≤u≤340∘. Since tan60∘=3, the principal solution is u=60∘. Tangent has a period of 180∘, so the solutions for u within [−20∘,340∘] are: u=60∘,u=60∘+180∘=240∘ Now solve for x=2u+20∘: 1. For u=60∘: x=260∘+20∘=40∘. 2. For u=240∘: x=2240∘+20∘=130∘. Both solutions lie within [0∘,180∘]. Thus x=40∘ or x=130∘.
📝 Chapter Quiz
6
Differentiation & Integration
📌 Differentiation & IntegrationP1 · Gradient & stationary points · Tangent & normal · Definite integral & area under curve
The gradient of a curve from first principles, the power rule for differentiation, and reversing it to integrate.
▲ Reference — The power rule
dxdxn=nxn−1; the gradient at a point is the value of dxdy there. Integration reverses this: ∫xndx=n+1xn+1+C for n=−1.
The amber line is a secant from x=1 to x=1+h on y=x2. Shrink h and watch its slope approach the tangent gradient, 2.
⊙ Explorer · Secant → tangentinteractive
Sampled points on f(x) = x²
x
f(x)
secant gradient—
The secant gradient is 2+h; as h→0 it tends to the tangent gradient 2.
Differentiate
nxn−1
Gradient
value of dxdy
Integrate
n+1xn+1+C
Definite
F(b)−F(a)
Cubic curve y=x3−3x showing local maximum at (−1,2) and local minimum at (1,−2).
⚠ Common Traps & Exam Pitfalls
Algebraic preparation: Express all algebraic fractions and surds in index form before differentiating or integrating: x23=3x−2, 4x=4x1/2, 2x1=21x−1/2. Differentiating denominators directly without rewriting produces invalid derivatives.
Tangent vs Normal: The tangent line has gradient mtan=dxdy. The normal line is perpendicular, having gradient mnorm=−mtan1. Both lines pass through the exact same point (x1,y1) on the curve.
Area between curves: Area is ∫ab(ytop−ybottom)dx. If a curve crosses the x-axis within the limits of integration, integrating across the roots will result in positive and negative areas cancelling out. You must integrate each section separately and sum the positive areas.
Worked example 6.A
Differentiate y=x2+3x.
dxdy=2x+3.
Worked example 6.B
Evaluate ∫012xdx.
[x2]01=1.
A curve has equation y=2x3−9x2+12x+1. (a) Find the coordinates of both stationary points. (b) Determine the nature of each stationary point using the second derivative dx2d2y.
(a) Find dxdy: dxdy=6x2−18x+12 Set dxdy=0: 6(x2−3x+2)=0⇒6(x−1)(x−2)=0, giving x=1 and x=2. When x=1: y=2(1)−9(1)+12(1)+1=6. Point is (1,6). When x=2: y=2(8)−9(4)+12(2)+1=16−36+24+1=5. Point is (2,5). (b) Second derivative: dx2d2y=12x−18 At x=1: dx2d2y=12(1)−18=−6<0, so (1,6) is a local maximum. At x=2: dx2d2y=12(2)−18=+6>0, so (2,5) is a local minimum.
Find the exact area of the region enclosed between the curve y=4x−x2 and the line y=x.
Find points of intersection: 4x−x2=x⇒3x−x2=0⇒x(3−x)=0 The curves intersect at x=0 and x=3. Between 0 and 3, the curve y=4x−x2 lies above the line y=x. The enclosed area is: A=∫03[(4x−x2)−x]dx=∫03(3x−x2)dx Integrate: A=[23x2−3x3]03=(23(9)−327)−0=227−9=227−18=29=4.5
Find the equation of the normal to the curve y=x4+2x at the point where x=4.
Rewrite in index form: y=4x−1/2+2x. At x=4: y=4(4−1/2)+2(4)=4(21)+8=2+8=10. Point of contact is (4,10). Differentiate: dxdy=4(−21x−3/2)+2=−2x−3/2+2=−x3/22+2 At x=4: x3/2=(4)3=8. Thus: mtan=−82+2=−41+2=47 The normal has gradient mnorm=−7/41=−74. Using point (4,10): y−10=−74(x−4)⇒7(y−10)=−4(x−4)⇒7y−70=−4x+16⇒4x+7y−86=0
📝 Chapter Quiz
7
Statistics & Probability
📌 Statistics & ProbabilityS1 · Basic probability · Conditional probability · Tree diagrams · Venn diagrams
Summarising data with averages and spread, and the probability of simple events.
▲ Reference — Data & chance
Mean is total over count; the median is the middle of the ordered data; range is largest minus smallest. Probability =totalfavourable.
Mean
n∑x
Median
middle value
Range
max − min
Probability
totalfav
Venn diagram showing two independent events A and B with P(A)=0.4, P(B)=0.5, and P(A∩B)=0.2.
⚠ Common Traps & Exam Pitfalls
Mutually exclusive vs Independent: These two concepts are mutually contradictory for non-trivial events. Mutually exclusive means they cannot happen together: P(A∩B)=0. Independent means the occurrence of one does not affect the probability of the other: P(A∩B)=P(A)P(B). If P(A)>0 and P(B)>0, mutually exclusive events can never be independent.
Conditional probability denominator: In P(A∣B)=P(B)P(A∩B), the denominator is always the given condition P(B), never P(A).
Sampling without replacement: In successive draws without replacement, remember to reduce both the favorable count and the total count on second branches (e.g. 95×84).
Worked example 7.A
Find the mean of 2,4,6,8.
420=5.
Worked example 7.B
Find the median of 3,7,9,12,20.
9.
Events A and B are such that P(A)=0.6, P(B)=0.5, and P(A∪B)=0.8. Find P(A∩B), calculate P(A∣B), and determine whether A and B are independent.
1. Use the addition rule: P(A∪B)=P(A)+P(B)−P(A∩B)⇒0.8=0.6+0.5−P(A∩B)⇒P(A∩B)=1.1−0.8=0.3. 2. Conditional probability: P(A∣B)=P(B)P(A∩B)=0.50.3=0.6 3. Check for independence: P(A∩B)=0.3 and P(A)×P(B)=0.6×0.5=0.30. Since P(A∩B)=P(A)P(B) (or equivalently P(A∣B)=P(A)=0.6), events A and B are independent.
A bag contains 5 red and 4 green marbles. Three marbles are drawn at random without replacement. Find the probability that: (a) all three are red, (b) at least two are red.
Total marbles = 9. Number of ways to choose 3 marbles = (39)=3×2×19×8×7=84. (a) All 3 are red: (35)=10. Probability: P(all red)=8410=425≈0.119 (b) 'At least two red' means exactly 2 red and 1 green, or exactly 3 red: Ways for 2 red, 1 green: (25)×(14)=10×4=40. Ways for 3 red: (35)=10. Total favorable outcomes: 40+10=50. Probability: P(≥2 red)=8450=4225≈0.595
📝 Chapter Quiz
8
Functions: Composite & Inverse
📌 Functions: Composite & InverseP1 · Domain & range · Composite fg(x) · Inverse f−1(x) · Modulus function
Beyond graphs, AS treats functions formally — domain, range, composition and inverses.
▲ Reference — Functions
fg(x)=f(g(x)). The inverse f−1 reverses f and reflects its graph in the line y=x; the range of f is the domain of f−1.
Composite
fg(x)
Inverse
swap & solve
Reflection
in y=x
Range
domain of f−1
Linear function f(x)=2x−3 and its inverse f−1(x)=2x+3, intersecting at (3,3) along the reflection line y=x.
⚠ Common Traps & Exam Pitfalls
One-to-one condition for inverses: An inverse function f−1 exists if and only if f is one-to-one over its given domain. For a quadratic function f(x)=a(x−h)2+k, the domain must be restricted to one side of the vertex (either x≥h or x≤h). If the domain is all real numbers, the inverse does not exist.
Domain of f−1: The domain of f−1 is always the range of f. Stating x∈R when the original function had a bounded range (e.g. f(x)≥4) loses the final mark.
Order of composition:fg(x) denotes f(g(x)) — evaluate g first, then insert into f. In general, fg(x)=gf(x). Furthermore, for fg to be defined, the range of g must lie entirely within the domain of f.
Worked example 8.A
If f(x)=3x−2, find f−1(x).
f−1(x)=3x+2.
Worked example — Composite functions
Given f(x)=x+1 (x≥−1) and g(x)=2x−3, find (a) fg(x), (b) the range of fg.
(a) fg(x)=f(2x−3)=2x−3+1=2x−2, domain x≥1.
(b) As x≥1, 2x−2≥0, so range of fg is fg(x)≥0.
The function f is defined by f(x)=x2−6x+13 for x≥3. (a) State the range of f. (b) Find an expression for f−1(x) and state the domain and range of f−1.
(a) Complete the square: f(x)=(x−3)2−9+13=(x−3)2+4. Since x≥3, (x−3)2≥0, so the minimum value is f(3)=4. The range of f is f(x)≥4. (b) Set y=(x−3)2+4. Rearrange for x: y−4=(x−3)2⇒x−3=+y−4(since x≥3)x=3+y−4 Therefore, f−1(x)=3+x−4. Domain of f−1 is x≥4 (the range of f), and range of f−1 is f−1(x)≥3 (the domain of f).
Functions g and h are defined by g(x)=2x−1 for x∈R, and h(x)=x−26 for x=2. (a) Find an expression for hg(x) in simplest form. (b) Solve the equation hg(x)=g(x).
(a) Substitute g(x) into h: hg(x)=h(2x−1)=(2x−1)−26=2x−36(x=23) (b) Set hg(x)=g(x): 2x−36=2x−1⇒6=(2x−1)(2x−3) Expand the right-hand side: 6=4x2−8x+3⇒4x2−8x−3=0 Factor: (2x−3)(2x+1)=0. Since x=23 for hg(x) to be defined, the value x=23 is excluded. Therefore, the unique solution is 2x+1=0⇒x=−21.
📝 Chapter Quiz
9
Circular Measure
📌 Circular MeasureP1 · Radians ↔ degrees · Arc length s=rθ · Sector area A=21r2θ · Segment area
Angles measured in radians give clean formulas for arc length and sector area.
▲ Reference — Radians
180∘=π radians. Arc length s=rθ; sector area A=21r2θ, with θ in radians.
Convert
180∘=π
Arc length
s=rθ
Sector
21r2θ
Full turn
2π
Circle with centre O and radius r=8 cm, showing sector OAB subtending central angle θ=1.2 rad and chord AB.
⚠ Common Traps & Exam Pitfalls
Calculator in Radian mode: Formulas s=rθ, A=21r2θ, and AΔ=21r2sinθ are strictly valid only when θ is in radians. If your calculator is in degree mode when evaluating sin(1.2), you will evaluate the sine of 1.2∘ instead of 1.2 rad, wiping out all accuracy marks.
Perimeter of a sector: The perimeter of a sector consists of the curved arc length PLUS the two straight radii: P=rθ+2r. Overlooking the two radii (+2r) is the single most common slip in Cambridge circular measure questions.
Major vs Minor: Always double check whether the question specifies the minor or major segment/sector. For the major sector, the central angle is 2π−θ.
Worked example 9.A
Find the arc length when r=5 and θ=3π.
s=5⋅3π=35π.
Worked example — Segment area
A sector OAB has radius 8 cm and angle ∠AOB=1.2 rad. Find the area of the minor segment cut off by chord AB.
A circle has radius 8 cm. A sector of this circle has a total perimeter of 28 cm. Find the angle of the sector in radians, and calculate the exact area of the sector.
The perimeter of a sector is given by P=s+2r=rθ+2r. Substitute P=28 and r=8: 28=8θ+2(8)⇒28=8θ+16⇒8θ=12⇒θ=812=1.5 radians The area of the sector is: A=21r2θ=21(82)(1.5)=21(64)(1.5)=32×1.5=48 cm2
In a circle of radius 10 cm, chord AB subtends an angle of θ=32π radians at the centre O. Find: (a) the exact length of chord AB, (b) the exact area of the minor segment bounded by chord AB and minor arc AB, in terms of π and 3.
(a) Use the cosine rule in triangle OAB with OA=OB=10 and ∠AOB=32π=120∘: AB2=102+102−2(10)(10)cos(32π)=100+100−200(−21)=200+100=300 Thus AB=300=103 cm. (b) Area of sector OAB: Asector=21r2θ=21(102)(32π)=3100π cm2 Area of triangle OAB: AΔ=21r2sinθ=21(102)sin(32π)=50(23)=253 cm2 Area of minor segment: Asegment=Asector−AΔ=3100π−253=3100π−753 cm2
📝 Chapter Quiz
10
Series & the Binomial Theorem
📌 Series & Binomial TheoremP1 · AP & GP formulas · Sum to infinity · (a+b)n expansion · General term
Arithmetic and geometric progressions, and the binomial expansion of (a+b)n.
▲ Reference — Series
AP sum Sn=2n(2a+(n−1)d); GP sum Sn=1−ra(1−rn); binomial (1+x)n=1+nx+2n(n−1)x2+⋯.
AP term
a+(n−1)d
AP sum
2n(2a+(n−1)d)
GP sum
1−ra(1−rn)
Binomial
nCr
Decaying terms of a convergent geometric sequence with a=12 and r=32, approaching zero with sum to infinity S∞=36.
⚠ Common Traps & Exam Pitfalls
Convergence condition for S∞: The sum to infinity S∞=1−ra is valid if and only if ∣r∣<1 (−1<r<1). If a question states that a series has a sum to infinity, you can establish an inequality for unknown parameters: −1<r<1.
Binomial powers on coefficients: In (a+bx)n, the term involving xr contains (bx)r=brxr. Writing 3x2 instead of (3x)2=9x2 or −2x3 instead of (−2x)3=−8x3 destroys the coefficient.
Term formulas index offset: In an AP, the n-th term has n−1 common differences: un=a+(n−1)d. In a GP, un=arn−1. Do not confuse the n-th term with the sum Sn.
Worked example 10.A
Find the sum of the first 10 terms of 2,5,8,…
S10=210(4+27)=155.
Worked example — Geometric series & sum to infinity
A geometric series has first term 12 and common ratio 32. Find (a) the 5th term, (b) S∞.
(a) u5=12⋅(32)4=12⋅8116=2764.
(b) S∞=1−3212=3112=36.
In an arithmetic progression, the 3rd term is 14 and the 7th term is 34. (a) Find the first term a and the common difference d. (b) Find the sum of the first 25 terms.
(a) Use un=a+(n−1)d: u3=a+2d=14u7=a+6d=34 Subtract the first equation from the second: 4d=20⇒d=5. Substitute back: a+2(5)=14⇒a=4. (b) Use the sum formula Sn=2n(2a+(n−1)d) with n=25: S25=225(2(4)+24(5))=225(8+120)=225(128)=25×64=1600
Find the coefficient of x3 in the expansion of (2−3x)(1+2x)6.
Expand (1+2x)6 up to the x3 term: (06)=1(16)(2x)=6(2x)=12x(26)(2x)2=15(4x2)=60x2(36)(2x)3=20(8x3)=160x3 So (1+2x)6=1+12x+60x2+160x3+⋯ Now multiply by (2−3x). The x3 term comes from: 2(160x3)+(−3x)(60x2)=320x3−180x3=140x3 Thus, the coefficient of x3 is 140.
Mechanics begins with motion in a straight line under constant acceleration.
▲ Reference — suvat equations
For constant acceleration: v=u+at, s=ut+21at2, v2=u2+2as. Velocity is the derivative of displacement; acceleration the derivative of velocity.
Velocity
v=u+at
Displacement
ut+21at2
No time
v2=u2+2as
Acceleration
dtdv
Velocity–time trapezoid graph: uniform acceleration from 0 to 20 m/s in 5 s, constant velocity for 10 s, and uniform deceleration to rest in 5 s. Total displacement is the trapezoid area: 210+20×20=300 m.
⚠ Common Traps & Exam Pitfalls
SUVAT vs Calculus: SUVAT formulas apply ONLY when acceleration is constant. If velocity or acceleration varies with time (e.g. v=3t2−12t), SUVAT yields zero marks — you must differentiate (a=dtdv) or integrate (s=∫vdt).
Velocity-Time graphs: Gradient equals acceleration (a=ΔtΔv). Total area under the graph equals displacement. For distance vs displacement: if the graph drops below the time axis (negative velocity), distance sums the absolute areas, whereas displacement nets them.
Vertical motion sign convention: Fix a reference direction at the start (usually upwards positive). Under this convention, acceleration is a=−g=−9.8 m/s2 (or −9.81). Any position below the launch point corresponds to negative displacement s<0.
Worked example 11.A
With u=0, a=2, t=3, find v.
v=0+2(3)=6.
Worked example — Calculus kinematics
A particle moves so that its velocity at time t s is v=3t2−12t+9 m/s. Find (a) the acceleration at t=2, (b) when the particle is momentarily at rest.
(a) a=dtdv=6t−12. At t=2: a=0 m/s².
(b) v=0⇒3(t−1)(t−3)=0⇒t=1 s or t=3 s.
A train accelerates uniformly from rest to 30 m/s in 20 s, travels at constant speed 30 m/s for 60 s, and then decelerates uniformly to rest in 15 s. Find: (a) the acceleration in the first phase, (b) the total distance travelled, (c) the average speed for the entire journey.
(a) a1=tv−u=2030−0=1.5 m/s2. (b) Total distance is the area of the trapezoid on the v-t graph with parallel sides 60 s and 20+60+15=95 s, and height 30 m/s: s=260+95×30=2155×30=155×15=2325 m (c) Average speed: Average speed=Total timeTotal distance=95 s2325 m≈24.47 m/s≈24.5 m/s (3 s.f.)
A stone is thrown vertically upwards with speed 15 m/s from the top of a cliff 40 m above sea level. Taking g=9.8 m/s2 and upwards as positive: (a) find the maximum height reached above the cliff, (b) calculate the time taken for the stone to reach the sea.
(a) At maximum height, v=0. u=+15 m/s, a=−9.8 m/s2: v2=u2+2as⇒0=152+2(−9.8)s⇒19.6s=225⇒s=19.6225≈11.48 m≈11.5 m (b) At the sea, the displacement relative to the launch point is s=−40 m. Use s=ut+21at2: −40=15t+21(−9.8)t2⇒−40=15t−4.9t2⇒4.9t2−15t−40=0 Solve via quadratic formula: t=2(4.9)15±(−15)2−4(4.9)(−40)=9.815±225+784=9.815±1009 Since 1009≈31.765, and t>0: t=9.815+31.765=9.846.765≈4.77 s (3 s.f.)
📝 Chapter Quiz
12
Forces & Equilibrium
📌 Forces & EquilibriumM1 · Resultant force · Resolving into components · Lami's theorem · Friction F=μR
Types of Forces
Weight W=mg, Normal reaction N, Tension T, Friction F≤μN. Forces are vectors — resolve horizontally and vertically.
Equilibrium
A particle is in equilibrium when the resultant force is zero: ∑Fx=0 and ∑Fy=0. Use triangle/polygon of forces.
Resolving Forces
Force F at angle θ: horizontal component Fcosθ, vertical component Fsinθ.
Friction
Limiting friction: F=μN. When moving: F=μN. Static: F≤μN. μ is the coefficient of friction.
Lami's Theorem
For three concurrent forces in equilibrium: sinαF1=sinβF2=sinγF3
Inclined Planes
On slope at angle α: component along slope =mgsinα, perpendicular =mgcosα.
▲ Forces & Equilibrium — Reference
A force is a vector (magnitude + direction). The resultant of forces is found by vector addition; for equilibrium the resultant is zero. Resolve forces into horizontal and vertical components: Fx=Fcosθ, Fy=Fsinθ. Friction force satisfies F≤μR; limiting equilibrium: F=μR.
Resolving
Fx=Fcosθ,Fy=Fsinθ
Equilibrium
∑Fx=0&∑Fy=0
Friction (limiting)
F=μR
Resultant
R=Fx2+Fy2
Closed vector triangle of forces in equilibrium: Weight W=20 N, Tension T, and Normal reaction R summing to zero resultant.
⚠ Common Traps & Exam Pitfalls
Normal reaction is perpendicular to the plane: On an inclined plane of angle α, the normal reaction is R=mgcosα (if no other perpendicular forces act). Assuming R=mg on an inclined plane is an instant fatal error.
Gravity components on a slope: Gravity acts vertically downward. Its resolved components are mgsinα acting down the slope and mgcosα acting perpendicularly into the plane.
Friction is reactive: The friction force obeys F≤μR. It only equals μR when motion is impending (limiting equilibrium) or actively occurring. If a system is stationary and not on the verge of slipping, F balances whatever force opposes it, satisfying F<μR.
Worked example — Resolving forces in equilibrium
A particle is in equilibrium under three forces: 10 N acting due East, 8 N acting due North, and a third force F. Find the magnitude and direction of F.
For equilibrium: Fx=−10 N, Fy=−8 N.
∣F∣=100+64=164≈12.8 N,tanθ=108⇒θ=38.7° W of S.
Worked example — Friction on an inclined plane
A block of mass 5 kg lies on a rough plane inclined at 30° to the horizontal (μ=0.4, g=10 m/s²). Find the friction force acting when the block is on the point of sliding down.
Normal reaction: R=5gcos30°=50×23≈43.3 N.
Friction (limiting, up the slope): F=0.4×43.3≈17.3 N.
Check: Gravity component down slope =50sin30°=25 N >F, so block would slide — friction acts up slope.
A block of mass 8 kg rests in limiting equilibrium on a rough plane inclined at 30∘ to the horizontal. Taking g=9.8 m/s2: (a) calculate the normal reaction R, (b) find the coefficient of friction μ between the block and the plane.
(a) Resolve perpendicular to the inclined plane: R=mgcos30∘=8(9.8)cos30∘=78.4×23=39.23≈67.9 N (3 s.f.) (b) Resolve parallel to the plane. Since the block is in limiting equilibrium on the verge of sliding down, friction F=μR acts up the plane: F=mgsin30∘=8(9.8)sin30∘=78.4×0.5=39.2 N Setting F=μR: μ=RF=mgcos30∘mgsin30∘=tan30∘=31=33≈0.577 (3 s.f.)
A small particle of weight 24 N is held in equilibrium by two light inextensible strings. String A makes an angle of 30∘ with the upward vertical, and string B makes an angle of 60∘ with the upward vertical. Find the tensions TA and TB in the two strings.
Notice that the angle between string A and string B is 30∘+60∘=90∘, so the strings are perpendicular. Resolve horizontally: TAsin30∘=TBsin60∘⇒TA(0.5)=TB(23)⇒TA=3TB Resolve vertically: TAcos30∘+TBcos60∘=24⇒TA(23)+TB(0.5)=24 Substitute TA=3TB: (3TB)(23)+0.5TB=24⇒23TB+21TB=24⇒2TB=24⇒TB=12 N Then: TA=123≈20.8 N (3 s.f.)
N1: A body remains at rest or in uniform motion unless acted on by a net force. N2:F=ma (net force = mass × acceleration). N3: For every action there is an equal and opposite reaction. For connected particles (e.g. Atwood's machine), consider each particle separately; the tension T is the same throughout an inextensible string over a smooth pulley.
Newton's 2nd Law
Fnet=ma
Atwood's machine
a=m1+m2(m1−m2)g
Tension (same string)
Same T throughout
Weight
W=mg
Velocity–time graph of connected particles m1=5 kg and m2=3 kg accelerating at a=5+35−3(9.8)=2.45 m/s2.
⚠ Common Traps & Exam Pitfalls
Separate equations for connected bodies: Never attempt to guess internal forces in one step. Always write ΣF=ma separately for each particle in its direction of motion. Adding the equations cancels the internal tension T and yields a immediately.
Assumptions and vocabulary: Cambridge papers frequently ask for the physical significance of modeling assumptions: 'Light' means string/pulley mass is negligible; 'Inextensible' means accelerations of both particles have the same magnitude; 'Smooth' means tension T is uniform across both sides.
Force exerted on the pulley: For two vertical hanging strings, the total downward force on the pulley is 2T. If one string is horizontal along a table and the other hangs vertically, the resultant force on the pulley is T2+T2=T2 at 45∘.
Worked example — Single particle on a surface
A force of 30 N acts on a 6 kg box on a rough horizontal surface (μ=0.3, g=10 m/s²). Find the acceleration.
Worked example — Connected particles over a pulley
Two particles of mass 4 kg and 6 kg are connected by a light inextensible string over a smooth pulley. Find the acceleration and the tension in the string (g=10 m/s²).
Taking down as positive for the 6 kg particle:
6g−T=6a,T−4g=4a.Adding: 2g=10a⇒a=2 m/s2,T=4(10+2)=48 N.
Two particles P of mass 3 kg and Q of mass 5 kg are connected by a light inextensible string passing over a smooth fixed pulley. The system is held at rest and released. Taking g=9.8 m/s2: (a) find the acceleration a of the system, (b) calculate the tension T in the string, (c) find the force exerted by the string on the pulley.
(a) Write F=ma for each particle in its direction of motion: For Q (moving downwards): 5g−T=5a For P (moving upwards): T−3g=3a Add the equations: 2g=8a⇒a=82(9.8)=2.45 m/s2 (b) Substitute a into the equation for P: T=3g+3a=3(9.8+2.45)=3(12.25)=36.75 N≈36.8 N (c) The pulley supports two vertical segments of string with tension T, so the total downward force on the pulley is: Fpulley=2T=2(36.75)=73.5 N
A block of mass 4 kg is pulled along a rough horizontal plane (μ=0.25) by a pulling force of magnitude 25 N acting at 30∘ above the horizontal. Taking g=9.8 m/s2: (a) show that the normal reaction R=26.7 N, (b) find the acceleration of the block.
(a) Resolve vertically (equilibrium in vertical direction): R+25sin30∘=mg⇒R+25(0.5)=4(9.8)⇒R+12.5=39.2⇒R=26.7 N (b) Limiting friction force opposes motion: F=μR=0.25×26.7=6.675 N Resolve horizontally using Fnet=ma: 25cos30∘−F=ma⇒25(23)−6.675=4a21.651−6.675=4a⇒14.976=4a⇒a=414.976≈3.74 m/s2 (3 s.f.)
Gravitational PE: GPE=mgh. Change in GPE: ΔGPE=mgΔh.
Conservation of Energy
KE+PE=constant (no friction). With friction: ΔKE+ΔPE+Wfriction=0.
Power
P=tW=Fv. Units: Watts (W). Maximum speed when driving force = resistance: P=Fresistance⋅vmax.
Efficiency
efficiency=power inputuseful power output×100%
▲ Energy, Work & Power — Reference
Kinetic energy:KE=21mv2. Gravitational PE:GPE=mgh. Work-energy principle: net work done = change in KE. Work done by a force:W=Fdcosθ. Power:P=tW=Fv. Conservation of energy: KE1+GPE1=KE2+GPE2 (no friction).
Kinetic energy
21mv2
Gravitational PE
mgh
Work done
Fdcosθ
Power
P=Fv
Quadratic relationship between kinetic energy and speed KE=21mv2 for a 2 kg mass. Doubling speed quadruples the kinetic energy.
⚠ Common Traps & Exam Pitfalls
Double-counting gravity: In energy equations, you either account for gravity through Gravitational Potential Energy (ΔKE+ΔPE=Wexternal) OR through work done by gravity (ΔKE=Wg+Wfriction+…). Including both simultaneously counts gravitational work twice.
Driving force vs Net force in P=Fv: The force in P=Fv is the tractive/driving force produced by the engine, NOT the resultant force. At maximum or steady velocity, acceleration is zero, so the driving force exactly equals the total opposing resistance (Fdrive=R+mgsinα).
Work against friction: Work done against friction is W=F×d (where d is the distance along the surface). This mechanical energy converts irreversibly into heat.
Worked example — Work-energy principle
A 2 kg ball rolls down a smooth slope of height 5 m from rest. Find its speed at the bottom (g=10 m/s²).
Loss in GPE=Gain in KE:2×10×5=21×2×v2⇒v2=100⇒v=10 m/s.
Worked example — Power
A car of mass 900 kg moves at constant speed 30 m/s against a resistance of 500 N. Find the power output of the engine.
At constant speed, driving force = resistance = 500 N.
P=Fv=500×30=15000 W=15 kW.
A car of mass 1200 kg ascends a hill of inclination α, where sinα=201, against a constant resistance to motion of 500 N. Taking g=9.8 m/s2: (a) find the driving force required to travel at a steady speed of 25 m/s, (b) calculate the power developed by the engine in kilowatts.
(a) Component of weight down the slope: W∥=mgsinα=1200(9.8)(201)=60(9.8)=588 N Since the car travels at steady speed (acceleration a=0), the engine driving force balances all resistance: Fdrive=Resistance+mgsinα=500+588=1088 N (b) Power output: P=Fdrive×v=1088×25=27200 W=27.2 kW
A block of mass 5 kg is released from rest at the top of a rough plane inclined at 30∘ to the horizontal. The length of the incline is 8 m and the coefficient of friction is μ=0.2. Using the work-energy principle and taking g=9.8 m/s2, calculate the speed of the block at the bottom of the incline.
1. Vertical height descended: h=8sin30∘=8(0.5)=4 m. Initial gravitational potential energy: PE=mgh=5(9.8)(4)=196 J 2. Normal reaction: R=mgcos30∘=5(9.8)(23)=24.53 N. Friction force: F=μR=0.2(24.53)=4.93 N. Work done against friction over distance d=8 m: Wfric=F×d=(4.93)×8=39.23≈67.896 J 3. By work-energy principle: Gain in KE=Loss in PE−Wfric⇒21mv2=196−67.896=128.104 J Substitute m=5 kg: 2.5v2=128.104⇒v2=2.5128.104=51.2416⇒v=51.2416≈7.16 m/s (3 s.f.)
Frequency density = frequency ÷ class width. Area of bar represents frequency. Used for continuous grouped data.
Cumulative Frequency
Ogive (cumulative frequency curve). Read median at n/2, Q1 at n/4, Q3 at 3n/4.
Measures of Location
Mean xˉ=∑f∑fx, Median (middle value), Mode (most frequent). For grouped data use midpoint.
Measures of Spread
Range, IQR, Variance σ2=n∑fx2−xˉ2, Standard deviation σ.
▲ Representation of Data — Reference
For grouped data with n values: meanxˉ=∑f∑fx; varianceσ2=∑f∑fx2−xˉ2; standard deviationσ=Var. In a histogram (unequal class widths), plot frequency density =freq/class width. In a cumulative frequency graph, the median is the 2nth value, Q1 is the 4nth, Q3 is the 43nth.
Mean (grouped)
xˉ=∑f∑fx
Variance
∑f∑fx2−xˉ2
Freq. density
freq ÷ class width
IQR
Q3−Q1
Box-and-whisker plot displaying Five-Number Summary: Min = 12, Q1 = 28, Median = 44, Q3 = 62, Max = 85 with IQR = 34.
⚠ Common Traps & Exam Pitfalls
Histograms with unequal class widths: The vertical axis must ALWAYS represent frequency density (frequency÷class width), never raw frequency. The area of each rectangle represents frequency.
Linear coding of data: If data values x are transformed via y=ax+b: • Mean scales and shifts: yˉ=axˉ+b • Variance scales by a2 only: Var(y)=a2Var(x) (the additive constant b does not affect spread) • Standard deviation scales by ∣a∣: σy=∣a∣σx.
Variance formula accuracy: When calculating σ2=n∑x2−xˉ2, never round xˉ prematurely before squaring; keep exact fractions or high precision to avoid severe cancellation errors.
Worked example — Mean and variance from table
Scores: 1 (freq 2), 2 (freq 5), 3 (freq 8), 4 (freq 3), 5 (freq 2). Find the mean and standard deviation.
∑f=20, ∑fx=2+10+24+12+10=58. Mean =58/20=2.9.
∑fx2=2+20+72+48+50=192. Var =192/20−2.92=9.6−8.41=1.19. SD ≈1.09.
Worked example — Cumulative frequency
Data range 0–50. Cumulative frequencies at 10,20,30,40,50 are 5,18,34,44,50. Estimate the median and IQR.
Median at n/2=25th value: read from cf graph at cf=25 → ≈27. Q1 at cf=12.5 → ≈18. Q3 at cf=37.5 → ≈33. IQR≈15.
A data set has mean 12 and standard deviation 4. A new value of 20 is added to n=9 existing values. Without finding the new variance, find the new mean.
Old sum =9×12=108. New sum =108+20=128. New mean =128/10=12.8.
A continuous dataset is grouped into class intervals. The interval 20≤x<35 has a frequency of 45. Find the frequency density for this class.
Class width w=35−20=15. Frequency density =class widthfrequency=1545=3.0. In a histogram, the height of the bar drawn on the interval [20,35) is 3.0.
16
Permutations & Combinations
📌 Permutations & CombinationsS1 · Factorial · nPr · nCr · Arrangements with identical items or restrictions
Factorial
n!=n×(n−1)×⋯×2×1. Convention: 0!=1.
Permutations
Ordered arrangements: nPr=(n−r)!n!. Order matters. n objects in a line: n! ways.
Combinations
Unordered selections: nCr=(rn)=r!(n−r)!n!. Order does not matter.
Restrictions
Always together: treat as one unit, then (n−1)!×r!. Never together: total − (always together).
Circular Arrangements
(n−1)! ways to arrange n objects in a circle (one position is fixed).
Identical Objects
Arrangements of n objects with repeats: a!b!c!⋯n!
▲ Permutations & Combinations — Reference
Permutation (order matters): nPr=(n−r)!n!. Combination (order does not matter): nCr=(rn)=r!(n−r)!n!. Arrangements with identical items: divide by the factorial of each repeated item. With restrictions: fix the restricted items first, then arrange the rest.
Permutation
nPr=(n−r)!n!
Combination
nCr=r!(n−r)!n!
Identical items
a!b!⋯n!
Fix & arrange
Fix restricted → count rest
Combinations (r6) for r=0,1,…,6, displaying the symmetric binomial coefficient distribution peaking at r=3.
⚠ Common Traps & Exam Pitfalls
Permutation vs Combination: If order or role matters (e.g. President and Vice President, line order, distinct positions), use permutations nPr. If order does not matter (e.g. selecting a committee of 3 students), use combinations nCr.
Identical items vs Distinct slots: Arranging n objects where some are identical requires dividing by each repeat count: p!q!⋯n!.
'Together' vs 'Separated': For items that must stay together, glue them as a single super-element and arrange (n−k+1)!, then multiply by k! for internal order. For items that must NEVER be adjacent, arrange the unrestricted items first, creating slots ⋆⋆…, and choose slot positions.
Worked example — Combinations with restrictions
A committee of 4 is chosen from 5 men and 6 women. Find the number of ways if the committee must contain at least 2 women.
📌 Discrete Random VariablesS1 · Probability distribution table · E(X) · Var(X) · Linear transforms E(aX+b)
Probability Distribution
Table of x values and corresponding P(X=x). Must satisfy: ∑P(X=x)=1 and P(X=x)≥0.
Expectation
E(X)=∑x⋅P(X=x)=μ. Also E(aX+b)=aE(X)+b.
Variance
Var(X)=E(X2)−[E(X)]2 where E(X2)=∑x2P(X=x). Also Var(aX+b)=a2Var(X).
Standard Deviation
σ=Var(X). Measures spread around the mean.
Uniform Distribution
Each value equally likely. If X takes values 1,2,…,n: E(X)=2n+1, Var(X)=12n2−1.
Combined Variables
E(X+Y)=E(X)+E(Y). If independent: Var(X+Y)=Var(X)+Var(Y).
▲ Discrete Random Variables — Reference
A discrete random variableX has a probability distribution with ∑P(X=x)=1. Expectation:E(X)=∑xP(X=x). Variance:Var(X)=E(X2)−[E(X)]2 where E(X2)=∑x2P(X=x). For linear transforms: E(aX+b)=aE(X)+b; Var(aX+b)=a2Var(X).
E(X)
∑xP(X=x)
Var(X)
E(X2)−[E(X)]2
E(aX+b)
aE(X)+b
Var(aX+b)
a2Var(X)
Probability distribution of a discrete random variable X taking values {1,2,3,4} with ∑P(X=x)=1.0.
⚠ Common Traps & Exam Pitfalls
Variance formula trap: Remember Var(X)=E(X2)−[E(X)]2. Do not forget to square E(X), and do not compute E(X2)−E(X).
Linear coding of variance:Var(aX+b)=a2Var(X). Notice that the constant b is eliminated completely, and a negative multiplier a becomes positive due to squaring (e.g. Var(5−2X)=(−2)2Var(X)=4Var(X)).
Sum of probabilities: The total probability MUST sum to 1: ∑P(X=x)=1. Always verify this condition first when solving for unknown parameters p or k.
Worked example — Finding E(X) and Var(X)
A biased die shows: P(1)=0.1,P(2)=0.2,P(3)=0.3,P(4)=0.3,P(5)=0.1. Find E(X) and Var(X).
Fixed number of trials n; each trial has two outcomes (success/failure); constant probability p; trials independent. Then X∼B(n,p).
Probability Formula
P(X=r)=(rn)pr(1−p)n−r for r=0,1,2,…,n.
Mean and Variance
E(X)=np, Var(X)=np(1−p), σ=np(1−p).
Cumulative Probabilities
Use tables or calculator: P(X≤r). Note: P(X≥r)=1−P(X≤r−1).
Normal Approximation
If n large and p close to 0.5: X≈N(np,np(1−p)) with continuity correction.
Finding Unknown n or p
Set up equations using given probabilities and solve. May require trial and error or logarithms for n.
▲ Binomial Distribution — Reference
If X∼B(n,p): n independent trials, each with probability p of success. P(X=r)=(rn)pr(1−p)n−r. Mean:E(X)=np. Variance:Var(X)=np(1−p). Use the binomial distribution when: fixed n, trials independent, constant p, only 2 outcomes (success/failure).
P(X=r)
(rn)pr(1−p)n−r
Mean
np
Variance
np(1−p)
Conditions
Fixed n, independent, constant p
Binomial distribution X∼B(5,0.4) probability distribution across r=0,1,2,3,4,5.
⚠ Common Traps & Exam Pitfalls
Inequality bounds for discrete distributions: Unlike continuous variables, strict inequalities make a critical difference: • P(X≥r)=1−P(X≤r−1) (NOT 1−P(X≤r)) • P(X>r)=1−P(X≤r) • P(X<r)=P(X≤r−1).
'At least one' complement shortcut:P(X≥1)=1−P(X=0)=1−(1−p)n. Always look for this time-saving identity in exam questions.
Four binomial conditions: Cambridge exam questions frequently ask you to state assumptions justifying the binomial model: (1) Fixed number of trials n, (2) Constant probability of success p, (3) Independent trials, (4) Exactly two mutually exclusive outcomes (success/failure).
In a manufacturing batch, 5% of components are defective. A sample of 12 components is inspected. Find the probability that at least 2 components are defective.
Let X∼B(12,0.05). We need P(X≥2)=1−[P(X=0)+P(X=1)]. P(X=0)=(0.95)12≈0.5404. P(X=1)=12(0.05)(0.95)11≈0.3413. Thus, P(X≥2)=1−(0.5404+0.3413)=1−0.8817=0.118 (3 s.f.).
📌 Normal DistributionS1 · X∼N(μ,σ2) · Standardising Z=σX−μ · Tables & symmetry · Finding μ or σ
The Normal Curve
Bell-shaped, symmetric about mean μ. X∼N(μ,σ2). Approximately 68%/95%/99.7% within 1/2/3 standard deviations.
Standardising
Z=σX−μ∼N(0,1). Use Z-tables (standard normal) to find probabilities.
Finding Probabilities
P(X<a)=Φ(σa−μ). Use symmetry: P(Z<−z)=1−P(Z<z).
Inverse Normal
Given probability, find the value. P(X<a)=p⇒a=μ+zσ where z=Φ−1(p).
Finding μ or σ
Set up two equations from given probabilities, solve simultaneously for unknown parameters.
Normal Approximation
To Binomial B(n,p): if n large, np>5, n(1−p)>5: use N(np,np(1−p)) with continuity correction ±0.5.
▲ Normal Distribution — Reference
If X∼N(μ,σ2): standardise with Z=σX−μ where Z∼N(0,1). Use tables (or calculator) for Φ(z)=P(Z≤z). Key symmetry: P(Z≤−z)=1−P(Z≤z). For inverse normal: given a probability, find the corresponding x value using x=μ+zσ.
Standardise
Z=σX−μ
Symmetry
P(Z≤−z)=1−Φ(z)
Inverse normal
x=μ+zσ
Normal approx to B
Use when n large, p≈0.5
Standard normal distribution curve Z∼N(0,1) with shaded region representing P(−1.5≤Z≤1.5)≈0.8664.
⚠ Common Traps & Exam Pitfalls
Variance vs Standard Deviation: Cambridge notation specifies X∼N(μ,σ2). When standardising Z=σX−μ, remember to divide by σ=σ2, NOT by σ2.
Negative z-values and tables: Standard normal tables provide Φ(z) only for z>0. By symmetry: Φ(−z)=1−Φ(z). For lower-tail probabilities P(Z<−1.25)=1−Φ(1.25).
Continuity correction (Normal approx to Binomial): When approximating discrete X∼B(n,p) by continuous Y∼N(np,np(1−p)): • P(X≥a)→P(Y>a−0.5) • P(X>a)→P(Y>a+0.5) • P(X≤a)→P(Y<a+0.5) • P(X=a)→P(a−0.5<Y<a+0.5).
The random variable X∼N(μ,σ2) satisfies P(X<65)=0.8413 and P(X<45)=0.0228. Find the values of μ and σ.
Standardising: Φ(σ65−μ)=0.8413⇒σ65−μ=1.0, so 65−μ=σ. For the lower tail: P(X<45)=0.0228⇒Φ(σ45−μ)=0.0228⇒σ45−μ=−2.0, so μ−45=2σ. Adding the two equations: 65−45=3σ⇒20=3σ⇒σ=6.67. Then μ=65−6.67=58.33.
Fifty AS-style problems across the Pure core plus statistics, tagged by difficulty. Click any problem for a full worked solution.
1
Simplify x3⋅x4.
Basic
x7.
2
Evaluate 2−3.
Intermediate
231=81.
3
Simplify 12.
Intermediate
4⋅3=23.
4
Rationalise 21.
Advanced
Multiply by 22:
22.
5
Simplify (x2)5.
Intermediate
x10.
6
Evaluate 271/3.
Advanced
327=3.
7
Solve x2=16.
Basic
x=±4.
8
Factor x2+5x+6.
Intermediate
(x+2)(x+3).
9
Solve x2−6x+8=0.
Intermediate
(x−2)(x−4)=0:
x=2,4.
10
Complete the square for x2+4x.
Intermediate
(x+2)2−4.
11
How many real roots does x2+x+1=0 have?
Advanced
Discriminant =1−4=−3<0:
none.
12
Find the sum of the roots of x2−5x+6=0.
Intermediate
2+3=5.
13
Solve 2x2−5x−3=0.
Advanced
(2x+1)(x−3)=0:
x=3,−21.
14
Find the vertex of y=x2−4x+3.
Intermediate
(x−2)2−1:
(2,−1).
15
Solve x+y=5, x−y=1.
Intermediate
Add: 2x=6:
x=3,y=2.
16
Solve 2x+y=8, y=x−1.
Intermediate
2x+x−1=8⇒x=3:
x=3,y=2.
17
Solve y=x2, y=x+2.
Advanced
x2−x−2=0⇒(x−2)(x+1)=0:
(2,4),(−1,1).
18
Solve 2x−3>5.
Intermediate
2x>8:
x>4.
19
Solve 3x+1≤10.
Intermediate
3x≤9:
x≤3.
20
Solve x2−4<0.
Advanced
−2<x<2.
21
Find the gradient through (1,2) and (4,11).
Intermediate
4−111−2=3.
22
Find the midpoint of (2,3) and (8,7).
Intermediate
(5,5).
23
Find the equation of the line with gradient 2 through (1,3).
Advanced
y−3=2(x−1):
y=2x+1.
24
Find the distance between (1,1) and (4,5).
Intermediate
9+16=5.
25
State the centre of (x−2)2+(y+3)2=25.
Advanced
(2,−3).
26
State the radius of x2+y2=49.
Intermediate
r=7.
27
Describe y=x2+3 relative to y=x2.
Intermediate
A translation 3 units up.
28
Describe y=(x−2)2 relative to y=x2.
Intermediate
A translation 2 units to the right.
29
Describe y=−x2 relative to y=x2.
Advanced
A reflection in the x-axis.
30
How does y=f(x)+k transform the graph of y=f(x)?
Intermediate
A vertical translation by k.
31
Evaluate sin30∘.
Intermediate
21.
32
Evaluate cos0∘.
Intermediate
1.
33
Evaluate tan45∘.
Intermediate
1.
34
Solve sinθ=21 for 0∘≤θ≤180∘.
Advanced
θ=30∘,150∘.
35
Simplify sin2θ+cos2θ.
Intermediate
1.
36
State the exact value of sin60∘.
Advanced
23.
37
Evaluate cos90∘.
Intermediate
0.
38
State the period of y=sinx.
Advanced
360∘.
39
Differentiate x2.
Intermediate
2x.
40
Differentiate x3.
Intermediate
3x2.
41
Differentiate 5x.
Intermediate
5.
42
Find dxdy for y=x2+3x.
Advanced
2x+3.
43
Find ∫2xdx.
Intermediate
x2+C.
44
Find ∫x2dx.
Advanced
3x3+C.
45
Find the gradient of y=x2 at x=3.
Intermediate
dxdy=2x=6:
6.
46
Evaluate ∫012xdx.
Advanced
[x2]01=1.
47
Find the mean of 2,4,6,8.
Intermediate
420=5.
48
Find the median of 3,7,9,12,20.
Intermediate
9.
49
A fair die is rolled. Find P(even).
Advanced
63=21.
50
Find the range of 5,9,2,11.
Intermediate
11−2=9.
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