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A2 Level Mathematics

Boards · Cambridge / Edexcel Level · A2 · Year 2 Chapters · 8 Explorers · 3 interactive
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About A2 Level

🗺 Cambridge A Level Mathematics 9709 — A2 Syllabus Map

PaperClipSAT ChapterKey Topics
P3 Pure 3Functions: Modulus & InverseModulus function, inverse, domain restriction
Exponentials & Logarithms\(e^x\), \(\ln x\), solving exponential equations, log graphs
Advanced TrigonometryCompound angle, double angle, R formula \(a\sin\theta+b\cos\theta\)
DifferentiationImplicit, parametric, related rates, product/quotient/chain
IntegrationBy parts, substitution, partial fractions, volumes of revolution
Sequences & SeriesMaclaurin series, binomial expansion for fractional/negative powers
Vectors3D vectors, dot product, angle between lines, equation of a plane
Algebra: Partial Fractions & DivisionPartial fractions (all cases), polynomial long division
Complex NumbersCartesian form, Argand diagram, modulus-argument, De Moivre
Numerical MethodsChange of sign, iterative sequences, Newton-Raphson
Differential EquationsSeparable DEs, integrating factor, forming DEs
S2 Statistics 2Poisson Distribution\(X\sim\text{Po}(\lambda)\), mean = variance = \(\lambda\), approximation to binomial
Continuous Random Variablespdf, cdf, \(E(X)\), \(\text{Var}(X)\), median, quartiles
Sampling & EstimationUnbiased estimators, CLT, confidence intervals for \(\mu\)
Hypothesis TestingOne/two-tailed tests for \(\mu\), Poisson mean, Binomial \(p\)

A2 is the second year of the A Level, completing courses such as Cambridge 9709 and Edexcel. It deepens Pure Mathematics and extends the applied content.

What it covers

Pure 2 & 3 brings modulus, composite and inverse functions, exponentials and logarithms, advanced trigonometry, the full rules of differentiation and integration, sequences and series (including the binomial expansion), and vectors.

Functions
modulus · inverse
Calculus
chain · product · quotient
Series
binomial · AP · GP
Vectors
2D & 3D
▲ How to use this course

Reference panels and worked examples sit beside three explorers — exponential behaviour, the tangent gradient and vector addition. Finish with the 50-problem set, then export it as a worksheet.

📝 Chapter Quiz
1

Functions: Modulus & Inverse

📌 Functions: Modulus & Inverse P3  ·  Modulus graph  ·  Inverse (domain restriction)  ·  Composite functions  ·  Graph of \(|f(x)|\)

The modulus function, composite functions, inverses, and domain and range.

▲ Reference — Functions

\( |x|=c \) gives \( x=\pm c \). A composite \( fg(x)=f(g(x)) \) is applied inside-out. The inverse \( f^{-1} \) reverses \( f \); swap \( x \) and \( y \) and solve. The range of \( f \) is the domain of \( f^{-1} \).

Modulus
\( |x|=\pm c \)
Composite
\( fg(x)=f(g(x)) \)
Inverse
swap \( x,y \) & solve
Range
output values
Worked example 1.A

Find the inverse of \( f(x)=2x+1 \).

Let \( y=2x+1 \), swap and solve:

\[ f^{-1}(x)=\tfrac{x-1}{2}. \]

Worked example 1.B

Solve \( |x-1|=3 \).

\[ x=4,\ -2. \]

Given \(f(x)=2x-3\) for \(x\in\mathbb{R}\), sketch \(y=|f(x)|\) and solve \(|2x-3|=5\).
Sketch: V-shape with vertex at \((1.5,0)\). Solve: \(2x-3=5\Rightarrow x=4\) or \(2x-3=-5\Rightarrow x=-1\).
📝 Chapter Quiz
2

Exponentials & Logarithms

📌 Exponentials & Logarithms P3  ·  \(e^x\) and \(\ln x\)  ·  Log laws  ·  Solving \(e^{ax+b}=k\)  ·  Log-linear graph to find unknowns

The exponential function \( e^{x} \), logarithms and their laws, and solving exponential equations.

▲ Reference — Exp & logs

\( \log_a(xy)=\log_a x+\log_a y \); \( \log_a(x^{n})=n\log_a x \). The natural log inverts the exponential: \( \ln(e^{x})=x \). To solve \( a^{x}=b \), take logs of both sides.

The curve is \( y=e^{kx} \): a positive \( k \) grows, a negative \( k \) decays. Slide \( k \) through zero to see it flip.

⊙ Explorer · Exponential growth & decayinteractive
behaviour
value at x = 1

All curves pass through \( (0,1) \); the sign of \( k \) sets growth versus decay.

Product law
\( \log_a x+\log_a y \)
Power law
\( n\log_a x \)
Natural log
\( \ln(e^{x})=x \)
Solve
take logs
Worked example 2.A

Evaluate \( \log_2 8 \).

\[ 2^{3}=8\Rightarrow 3. \]

Worked example 2.B

Solve \( 3^{x}=81 \).

\[ 3^{4}=81\Rightarrow x=4. \]

Given \(\ln y = 2\ln x + \ln 3\), express \(y\) in terms of \(x\). Hence sketch the graph.
\(\ln y=\ln x^2+\ln 3=\ln(3x^2)\Rightarrow y=3x^2\). Parabola through origin, scaled by 3.
📝 Chapter Quiz
3

Advanced Trigonometry

📌 Advanced Trigonometry P3  ·  Compound angle formulae  ·  Double angle  ·  \(R\sin(\theta+\alpha)\) form  ·  Solving equations in a range

Reciprocal ratios, the double-angle formulae, and solving trigonometric equations.

▲ Reference — Identities

\( \sec\theta=\dfrac{1}{\cos\theta} \). Double angle: \( \sin2\theta=2\sin\theta\cos\theta \) and \( \cos2\theta=2\cos^{2}\theta-1 \). The tangent curve has period \( 180^{\circ} \).

Reciprocal
\( \sec\theta=\tfrac{1}{\cos\theta} \)
Sine double
\( 2\sin\theta\cos\theta \)
Cosine double
\( 2\cos^{2}\theta-1 \)
Period of tan
\( 180^{\circ} \)
Worked example 3.A

Write \( \cos2\theta \) in terms of \( \cos\theta \).

\[ \cos2\theta=2\cos^{2}\theta-1. \]

Worked example 3.B

Solve \( \cos\theta=0 \) for \( 0^{\circ}\le\theta\le180^{\circ} \).

\[ \theta=90^{\circ}. \]

Express \(3\sin\theta+4\cos\theta\) in the form \(R\sin(\theta+\alpha)\) where \(R>0\) and \(0<\alpha<90°\).
\(R=\sqrt{9+16}=5\). \(\tan\alpha=4/3\Rightarrow\alpha=53.13°\). So \(5\sin(\theta+53.13°)\).
📝 Chapter Quiz
4

Differentiation

📌 Differentiation P3  ·  Implicit differentiation  ·  Parametric differentiation  ·  Product/quotient rule  ·  Related rates

Differentiating standard functions and applying the chain, product and quotient rules.

▲ Reference — Rules

\( \tfrac{d}{dx}e^{x}=e^{x} \), \( \tfrac{d}{dx}\ln x=\tfrac1x \), \( \tfrac{d}{dx}\sin x=\cos x \). Chain: \( \tfrac{dy}{dx}=\tfrac{dy}{du}\tfrac{du}{dx} \). Product: \( (uv)'=u'v+uv' \). Quotient: \( \left(\tfrac{u}{v}\right)'=\dfrac{u'v-uv'}{v^{2}} \).

Slide the point along \( y=x^{3}-3x \). The amber line is the tangent; its gradient is \( 3x^{2}-3 \).

⊙ Explorer · The tangent gradientinteractive
gradient dy/dx

The gradient is zero at the turning points, where \( 3x^{2}-3=0 \), i.e. \( x=\pm1 \).

Exponential
\( \tfrac{d}{dx}e^{x}=e^{x} \)
Chain
\( \tfrac{dy}{du}\tfrac{du}{dx} \)
Product
\( u'v+uv' \)
Quotient
\( \dfrac{u'v-uv'}{v^{2}} \)
Worked example 4.A

Differentiate \( y=(2x+1)^{3} \).

Chain rule:

\[ 3(2x+1)^{2}\cdot2=6(2x+1)^{2}. \]

Worked example 4.B

Differentiate \( y=\dfrac{x}{x+1} \).

\[ \frac{(x+1)-x}{(x+1)^{2}}=\frac{1}{(x+1)^{2}}. \]

A curve is defined parametrically by \(x=t^2+1\), \(y=2t^3-3t\). Find \(\dfrac{dy}{dx}\) in terms of \(t\) and the value at \(t=1\).
\(\dfrac{dx}{dt}=2t\), \(\dfrac{dy}{dt}=6t^2-3\). \(\dfrac{dy}{dx}=\dfrac{6t^2-3}{2t}\). At \(t=1\): \(\dfrac{3}{2}\).
📝 Chapter Quiz
5

Integration

📌 Integration P3  ·  Integration by parts  ·  Substitution  ·  Partial fractions  ·  Volumes of revolution

Integrating standard functions, definite integrals, and the area under a curve.

▲ Reference — Standard integrals

\( \displaystyle\int x^{n}\,dx=\dfrac{x^{n+1}}{n+1}+C \) (\( n\neq-1 \)); \( \displaystyle\int e^{x}\,dx=e^{x}+C \); \( \displaystyle\int\tfrac1x\,dx=\ln|x|+C \). A definite integral gives the signed area: \( F(b)-F(a) \).

Power
\( \tfrac{x^{n+1}}{n+1}+C \)
Exponential
\( e^{x}+C \)
Reciprocal
\( \ln|x|+C \)
Area
\( F(b)-F(a) \)
Worked example 5.A

Find \( \displaystyle\int 6x^{2}\,dx \).

\[ 2x^{3}+C. \]

Worked example 5.B

Find the area under \( y=x^{2} \) from \( 0 \) to \( 3 \).

\[ \left[\tfrac{x^{3}}{3}\right]_{0}^{3}=9. \]

Find \(\displaystyle\int x\sin x\,dx\).
Integration by parts: \(u=x\), \(dv=\sin x\,dx\Rightarrow v=-\cos x\). \(\int x\sin x\,dx=-x\cos x+\int\cos x\,dx=-x\cos x+\sin x+c\).
📝 Chapter Quiz
6

Sequences & Series

📌 Sequences & Series P3  ·  Maclaurin series  ·  Binomial expansion (fractional & negative)  ·  Convergence condition \(|x|<1\)

Arithmetic and geometric progressions, sums to infinity, and the binomial expansion.

▲ Reference — Progressions

AP term \( a+(n-1)d \); GP term \( ar^{\,n-1} \). A convergent GP \( (|r|<1) \) sums to \( \dfrac{a}{1-r} \). The sum of the first \( n \) integers is \( \dfrac{n(n+1)}{2} \).

AP term
\( a+(n-1)d \)
GP term
\( ar^{\,n-1} \)
GP to infinity
\( \dfrac{a}{1-r} \)
First n integers
\( \dfrac{n(n+1)}{2} \)
Worked example 6.A

Find the 10th term of \( 2,5,8,\dots \)

\( a=2,\ d=3 \):

\[ 2+9(3)=29. \]

Worked example 6.B

Find the sum to infinity of \( 1+\tfrac12+\tfrac14+\dots \)

\[ \frac{1}{1-\tfrac12}=2. \]

Find the first three non-zero terms of the Maclaurin series for \(e^{2x}\). State the range of validity.
\(e^{2x}=1+2x+\dfrac{(2x)^2}{2!}+\cdots=1+2x+2x^2+\cdots\). Valid for all \(x\in\mathbb{R}\).
📝 Chapter Quiz
7

Vectors

📌 Vectors P3  ·  3D column vectors  ·  Dot product  ·  Angle between lines  ·  Vector equation of a plane

Vector components, addition and scalar multiples, and the magnitude of a vector.

▲ Reference — Vectors

Add componentwise: \( (a_1,a_2)+(b_1,b_2)=(a_1+b_1,\,a_2+b_2) \). A scalar multiple stretches: \( k(a_1,a_2)=(ka_1,ka_2) \). Magnitude \( |\mathbf{v}|=\sqrt{a_1^{2}+a_2^{2}} \).

Vector \( \mathbf{a}=(3,1) \) is fixed (indigo). Slide the components of \( \mathbf{b} \) (amber); the dashed line is the resultant \( \mathbf{a}+\mathbf{b} \).

⊙ Explorer · Adding vectorsinteractive
resultant a + b
magnitude

The resultant is the diagonal of the parallelogram formed by \( \mathbf{a} \) and \( \mathbf{b} \).

Add
componentwise
Scalar multiple
\( (ka_1,ka_2) \)
Magnitude
\( \sqrt{a_1^{2}+a_2^{2}} \)
Unit vector
\( \tfrac{\mathbf{v}}{|\mathbf{v}|} \)
Worked example 7.A

Find \( (1,2)+(3,1) \).

\[ (4,\,3). \]

Worked example 7.B

Find the magnitude of \( (6,8) \).

\[ \sqrt{36+64}=10. \]

Lines \(\ell_1\) and \(\ell_2\) have direction vectors \(\mathbf{d_1}=\begin{pmatrix}2\\1\\-1\end{pmatrix}\) and \(\mathbf{d_2}=\begin{pmatrix}1\\-1\\3\end{pmatrix}\). Find the acute angle between them.
\(\mathbf{d_1}\cdot\mathbf{d_2}=2-1-3=-2\). \(|\mathbf{d_1}|=\sqrt6\), \(|\mathbf{d_2}|=\sqrt{11}\). \(\cos\theta=\dfrac{2}{\sqrt{66}}\Rightarrow\theta=\arccos\!\left(\dfrac{2}{\sqrt{66}}\right)\approx75.7°\).
📝 Chapter Quiz
8

Algebra: Partial Fractions & Division

📌 Algebra: Partial Fractions & Division P3  ·  Partial fractions (proper, improper, repeated, quadratic denominator)  ·  Polynomial long division

Polynomial division and partial fractions break complicated algebraic fractions into simpler pieces.

▲ Reference — Partial fractions

A proper fraction \( \tfrac{px+q}{(x+a)(x+b)} \) splits as \( \tfrac{A}{x+a}+\tfrac{B}{x+b} \). If the fraction is improper, divide first.

Linear factors
\( \tfrac{A}{x+a} \)
Repeated
\( \tfrac{A}{x+a}+\tfrac{B}{(x+a)^{2}} \)
Improper
divide first
Cover-up
find \( A,B \)
Worked example 8.A

Express \( \dfrac{1}{x(x+1)} \) in partial fractions.

\[ \frac{1}{x}-\frac{1}{x+1}. \]

Worked example — Improper partial fractions

Express \(\dfrac{x^3+2x}{x^2-1}\) in partial fractions (after division).

Degree of numerator ≥ denominator, so divide first: \(x^3+2x=(x^2-1)\cdot x+3x\). So:

\[\frac{x^3+2x}{x^2-1}=x+\frac{3x}{(x-1)(x+1)}=x+\frac{A}{x-1}+\frac{B}{x+1}.\]

Cover-up: \(A=\tfrac{3}{2}\), \(B=\tfrac{3}{2}\). Result: \(x+\dfrac{3/2}{x-1}+\dfrac{3/2}{x+1}\).

Express \(\dfrac{3x+1}{(x+1)(x-2)}\) in partial fractions.
\(\dfrac{A}{x+1}+\dfrac{B}{x-2}\). Cover-up: let \(x=2\): \(B=\tfrac{7}{3}\). Let \(x=-1\): \(A=\tfrac{-2}{-3}=\tfrac{2}{3}\). Answer: \(\dfrac{2/3}{x+1}+\dfrac{7/3}{x-2}\).
📝 Chapter Quiz
9

Complex Numbers

📌 Complex Numbers P3  ·  Cartesian \(a+bi\)  ·  Argand diagram  ·  Modulus-argument form  ·  Roots of polynomials

The imaginary unit \( i \) extends the reals; complex numbers add, multiply, and have a modulus and conjugate.

▲ Reference — Complex numbers

\( i^{2}=-1 \); \( z=a+bi \) has modulus \( |z|=\sqrt{a^{2}+b^{2}} \) and conjugate \( \bar{z}=a-bi \), with \( z\bar{z}=|z|^{2} \).

Unit
\( i^{2}=-1 \)
Form
\( a+bi \)
Modulus
\( \sqrt{a^{2}+b^{2}} \)
Conjugate
\( a-bi \)
Worked example 9.A

Find \( |3+4i| \).

\[ \sqrt{9+16}=5. \]

Worked example — Modulus-argument form

Write \(z=-1+\sqrt{3}\,i\) in modulus-argument form and find \(z^4\) using De Moivre's theorem.

\(|z|=\sqrt{1+3}=2\). \(\arg z=\pi-\arctan\sqrt{3}=\pi-\tfrac{\pi}{3}=\tfrac{2\pi}{3}\).

\(z=2\bigl(\cos\tfrac{2\pi}{3}+i\sin\tfrac{2\pi}{3}\bigr)\). By De Moivre: \(z^4=2^4\bigl(\cos\tfrac{8\pi}{3}+i\sin\tfrac{8\pi}{3}\bigr)=16\bigl(\cos\tfrac{2\pi}{3}+i\sin\tfrac{2\pi}{3}\bigr)=16(-\tfrac{1}{2}+\tfrac{\sqrt3}{2}i)=-8+8\sqrt3\,i\).

Given that \(z_1=3+4i\) and \(z_2=1-2i\), find \(\dfrac{z_1}{z_2}\) in the form \(a+bi\).
Multiply by conjugate: \(\dfrac{(3+4i)(1+2i)}{(1-2i)(1+2i)}=\dfrac{3+6i+4i-8}{1+4}=\dfrac{-5+10i}{5}=-1+2i\).
📝 Chapter Quiz
10

Numerical Methods

📌 Numerical Methods P3  ·  Interval bisection / change of sign  ·  Iterative formula \(x_{n+1}=g(x_n)\)  ·  Newton-Raphson

When an equation cannot be solved exactly, sign changes locate roots and iteration refines them.

▲ Reference — Finding roots

A sign change of \( f \) across \( [a,b] \) traps a root. Iteration \( x_{n+1}=g(x_n) \) converges when it settles; the Newton–Raphson step is \( x_{n+1}=x_n-\tfrac{f(x_n)}{f'(x_n)} \).

Sign change
root in \( [a,b] \)
Iteration
\( x_{n+1}=g(x_n) \)
Newton
\( x_n-\tfrac{f}{f'} \)
Converge
value settles
Worked example 10.A

For \( f(x)=x^{2}-2 \), between which integers does a root lie?

\[ 1\ \text{and}\ 2,\ \text{since}\ f(1)<0<f(2). \]

Worked example — Newton-Raphson

Use Newton-Raphson to find the root of \(f(x)=x^3-5\) near \(x_0=1.7\). Do one iteration.

\(f(x)=x^3-5\), \(f'(x)=3x^2\).

\[x_1=x_0-\frac{f(x_0)}{f'(x_0)}=1.7-\frac{1.7^3-5}{3(1.7)^2}=1.7-\frac{4.913-5}{8.67}=1.7-\frac{-0.087}{8.67}\approx1.710.\]

Show that \(x^3+2x-6=0\) has a root in \([1,2]\). Taking \(x_0=1.5\), perform one Newton-Raphson iteration.
\(f(1)=-3<0\), \(f(2)=6>0\): sign change confirms root. \(f(1.5)=1.5^3+3-6=-0.625\). \(f'(x)=3x^2+2\Rightarrow f'(1.5)=8.75\). \(x_1=1.5-\tfrac{-0.625}{8.75}\approx1.571\).
📝 Chapter Quiz
11

Differential Equations

📌 Differential Equations P3  ·  Separable variables  ·  Integrating factor  ·  Forming a DE from context

A differential equation relates a function to its rate of change; separable equations integrate directly.

▲ Reference — Separable equations

Write \( \tfrac{dy}{dx}=f(x)g(y) \) as \( \tfrac{1}{g(y)}\,dy=f(x)\,dx \) and integrate both sides; an initial condition fixes the constant.

Separate
variables
Integrate
both sides
Constant
\( +C \)
Condition
fixes \( C \)
Worked example 11.A

Solve \( \dfrac{dy}{dx}=y \).

\[ y=Ae^{x}. \]

Worked example — Integrating factor

Solve \(\dfrac{dy}{dx}+2y=e^x\).

Integrating factor: \(\mu=e^{\int2\,dx}=e^{2x}\). Multiply through: \(\dfrac{d}{dx}(ye^{2x})=e^{3x}\).

\[ye^{2x}=\int e^{3x}\,dx=\tfrac{1}{3}e^{3x}+c\;\Rightarrow\;y=\tfrac{1}{3}e^x+ce^{-2x}.\]

Solve the separable DE \(\dfrac{dy}{dx}=\dfrac{x+1}{y}\) given \(y=2\) when \(x=0\).
Separate: \(y\,dy=(x+1)\,dx\). Integrate: \(\tfrac{y^2}{2}=\tfrac{x^2}{2}+x+c\). At \((0,2)\): \(2=c\). So \(y^2=x^2+2x+4\).
📝 Chapter Quiz
S2·1

Poisson Distribution

📌 Poisson Distribution S2  ·  \(X\sim\text{Po}(\lambda)\)  ·  \(P(X=r)=e^{-\lambda}\lambda^r/r!\)  ·  Mean = Var = \(\lambda\)  ·  Poisson approx. to Binomial

Conditions

Events occur independently, at a constant average rate \(\lambda\), and singly in time/space. \(X\sim\text{Po}(\lambda)\).

Probability Formula

\(P(X=r)=\dfrac{e^{-\lambda}\lambda^r}{r!}\) for \(r=0,1,2,\ldots\)

Mean and Variance

\(E(X)=\text{Var}(X)=\lambda\). The mean equals the variance — a key identifying feature.

Cumulative Tables

Use Poisson tables for \(P(X\leq r)\). Note \(P(X\geq r)=1-P(X\leq r-1)\). Additive: \(X+Y\sim\text{Po}(\lambda_1+\lambda_2)\).

Changing the Interval

If \(X\sim\text{Po}(\lambda)\) per hour, then in \(t\) hours: \(X\sim\text{Po}(\lambda t)\).

Normal Approximation

If \(\lambda>15\): \(\text{Po}(\lambda)\approx N(\lambda,\lambda)\) with continuity correction.

▲ Poisson Distribution — Reference

If events occur at a constant average rate \(\lambda\) independently, \(X\sim\text{Po}(\lambda)\) with: \(P(X=r)=\dfrac{e^{-\lambda}\lambda^r}{r!}\) for \(r=0,1,2,\ldots\)  ·  \(E(X)=\lambda\), \(\text{Var}(X)=\lambda\). Poisson approximation to Binomial: if \(n\) is large, \(p\) is small, \(np=\lambda\) is moderate (\(n>50, p<0.1\)), then \(B(n,p)\approx\text{Po}(\lambda)\).

\(P(X=r)\)
\(\dfrac{e^{-\lambda}\lambda^r}{r!}\)
Mean = Var
\(\lambda\)
Sum of Poissons
\(X+Y\sim\text{Po}(\lambda_1+\lambda_2)\)
Binom approx
\(n>50,\,p<0.1,\,\lambda=np\)
Worked example — Exact probability

Faults in a wire occur at a rate of 2 per metre. Find the probability of (a) exactly 3 faults in 1 m, (b) fewer than 2 faults in 0.5 m.

(a) \(\lambda=2\): \(P(X=3)=\dfrac{e^{-2}\cdot8}{6}\approx0.1804\).

(b) \(\lambda=1\): \(P(X<2)=P(0)+P(1)=e^{-1}+e^{-1}=2e^{-1}\approx0.7358\).

Worked example — Binomial approximation

\(X\sim B(200,0.02)\). Use a Poisson approximation to find \(P(X=5)\).

\(\lambda=200\times0.02=4\). \(P(X=5)=\dfrac{e^{-4}\cdot4^5}{120}=\dfrac{1024e^{-4}}{120}\approx0.1563\).

Cars arrive at a toll booth at an average rate of 3 per minute. Find the probability that (a) exactly 5 arrive in one minute, (b) at least 2 arrive in 30 seconds.
(a) \(P(X=5)=\dfrac{e^{-3}\cdot243}{120}\approx0.1008\). (b) \(\lambda=1.5\): \(P(X\geq2)=1-P(0)-P(1)=1-e^{-1.5}-1.5e^{-1.5}=1-2.5e^{-1.5}\approx0.4422\).
S2·2

Continuous Random Variables

📌 Continuous Random Variables S2  ·  Probability density function  ·  CDF \(F(x)\)  ·  \(E(X)\) & \(\text{Var}(X)\)  ·  Median & quartiles

Probability Density Function

\(f(x)\geq0\) for all \(x\) and \(\displaystyle\int_{-\infty}^{\infty}f(x)\,dx=1\). \(P(a\leq X\leq b)=\displaystyle\int_a^b f(x)\,dx\).

Cumulative Distribution Function

\(F(x)=P(X\leq x)=\displaystyle\int_{-\infty}^{x}f(t)\,dt\). Differentiating: \(f(x)=F'(x)\).

Mean (Expectation)

\(E(X)=\displaystyle\int_{-\infty}^{\infty}xf(x)\,dx\). \(E(g(X))=\displaystyle\int g(x)f(x)\,dx\).

Variance

\(\text{Var}(X)=E(X^2)-[E(X)]^2\) where \(E(X^2)=\displaystyle\int x^2f(x)\,dx\).

Median and Percentiles

Median \(m\): \(F(m)=0.5\). \(p\)-th percentile \(x_p\): \(F(x_p)=p/100\).

Uniform Distribution

\(X\sim U(a,b)\): \(f(x)=\dfrac{1}{b-a}\), \(E(X)=\dfrac{a+b}{2}\), \(\text{Var}(X)=\dfrac{(b-a)^2}{12}\).

▲ Continuous Random Variables — Reference

A CRV \(X\) has a probability density function \(f(x)\geq0\) with \(\int_{-\infty}^{\infty}f(x)\,dx=1\). CDF: \(F(x)=P(X\leq x)=\int_{-\infty}^{x}f(t)\,dt\). Mean: \(E(X)=\int x\,f(x)\,dx\).   Variance: \(\text{Var}(X)=\int x^2f(x)\,dx-[E(X)]^2\). Median \(m\): solve \(F(m)=0.5\).   Mode: maximum of \(f(x)\).

pdf condition
\(\int f(x)\,dx=1\)
CDF
\(F(x)=\int_{-\infty}^{x}f(t)\,dt\)
E(X)
\(\int xf(x)\,dx\)
Var(X)
\(E(X^2)-[E(X)]^2\)
Worked example — Finding the constant

\(f(x)=kx(2-x)\) for \(0\leq x\leq2\), zero otherwise. Find \(k\), then \(E(X)\).

\[\int_0^2 kx(2-x)\,dx=k\int_0^2(2x-x^2)\,dx=k\left[x^2-\tfrac{x^3}{3}\right]_0^2=k\cdot\tfrac{4}{3}=1\Rightarrow k=\tfrac{3}{4}.\]\[E(X)=\int_0^2 x\cdot\tfrac{3}{4}x(2-x)\,dx=\tfrac{3}{4}\int_0^2(2x^2-x^3)\,dx=\tfrac{3}{4}\left[\tfrac{2x^3}{3}-\tfrac{x^4}{4}\right]_0^2=\tfrac{3}{4}\cdot\tfrac{4}{3}=1.\]

Worked example — CDF and median

With the same \(f(x)=\tfrac{3}{4}x(2-x)\) on \([0,2]\), find the CDF \(F(x)\) and the median.

\[F(x)=\int_0^x \tfrac{3}{4}t(2-t)\,dt=\tfrac{3}{4}\left[t^2-\tfrac{t^3}{3}\right]_0^x=\tfrac{3x^2}{4}-\tfrac{x^3}{4}.\]

Median: \(F(m)=\tfrac{1}{2}\Rightarrow\tfrac{3m^2}{4}-\tfrac{m^3}{4}=\tfrac{1}{2}\Rightarrow m^3-3m^2+2=0\). Try \(m=1\): \(1-3+2=0\) ✓. So median \(=1\).

\(f(x)=cx^2\) for \(0\leq x\leq3\), zero otherwise. Find \(c\), \(E(X)\), and \(P(1\leq X\leq2)\).
\(\int_0^3 cx^2\,dx=9c=1\Rightarrow c=\tfrac{1}{9}\). \(E(X)=\tfrac{1}{9}\int_0^3 x^3\,dx=\tfrac{1}{9}\cdot\tfrac{81}{4}=\tfrac{9}{4}\). \(P(1\leq X\leq2)=\tfrac{1}{9}\left[\tfrac{x^3}{3}\right]_1^2=\tfrac{1}{27}(8-1)=\tfrac{7}{27}\).
🔗 See also: Discrete RVs · Integration
S2·3

Sampling & Estimation

📌 Sampling & Estimation S2  ·  Random sampling  ·  Unbiased estimators \(\bar{x}\) and \(s^2\)  ·  Central Limit Theorem  ·  Confidence interval for \(\mu\)

Populations and Samples

Population: entire group of interest. Sample: subset used to make inferences. Random sampling ensures unbiased estimates.

Sample Mean Distribution

If \(X\sim N(\mu,\sigma^2)\) then \(\bar{X}\sim N\!\left(\mu,\dfrac{\sigma^2}{n}\right)\). Standard error \(=\dfrac{\sigma}{\sqrt{n}}\).

Unbiased Estimators

\(\bar{X}\) is unbiased for \(\mu\). Unbiased variance: \(s^2=\dfrac{1}{n-1}\sum(x_i-\bar{x})^2\).

Confidence Intervals

95% CI for \(\mu\): \(\bar{x}\pm z_{0.025}\cdot\dfrac{\sigma}{\sqrt{n}}\) where \(z_{0.025}=1.96\).

Interpretation

A 95% CI means: 95% of all such intervals constructed would contain the true \(\mu\). Not a probability statement about \(\mu\).

Sample Size

Width of CI \(\propto 1/\sqrt{n}\). To halve width, multiply \(n\) by 4. Required \(n\geq\left(\dfrac{z\sigma}{E}\right)^2\).

▲ Sampling & Estimation — Reference

An unbiased estimator of \(\mu\) is \(\bar{X}\). An unbiased estimator of \(\sigma^2\) is \(s^2=\dfrac{\sum(x_i-\bar{x})^2}{n-1}=\dfrac{\sum x_i^2-n\bar{x}^2}{n-1}\). CLT: For large \(n\), \(\bar{X}\sim N\!\left(\mu,\dfrac{\sigma^2}{n}\right)\) approximately. A 95% confidence interval for \(\mu\) (known \(\sigma\)): \(\bar{x}\pm1.96\dfrac{\sigma}{\sqrt{n}}\). Use \(z=2.576\) for 99% CI.

Unbiased \(\hat{\mu}\)
\(\bar{x}=\dfrac{\sum x}{n}\)
Unbiased \(\hat{\sigma}^2\)
\(s^2=\dfrac{\sum x^2-n\bar{x}^2}{n-1}\)
Dist. of \(\bar{X}\)
\(N\!\left(\mu,\dfrac{\sigma^2}{n}\right)\)
95% CI
\(\bar{x}\pm1.96\dfrac{\sigma}{\sqrt{n}}\)
Worked example — Confidence interval

A sample of 36 light bulbs has mean lifetime \(\bar{x}=1200\) hours. The population SD is known to be \(\sigma=60\) hours. Find a 95% CI for the population mean.

\[\bar{x}\pm1.96\cdot\frac{\sigma}{\sqrt{n}}=1200\pm1.96\cdot\frac{60}{\sqrt{36}}=1200\pm19.6.\]

95% CI: \((1180.4,\;1219.6)\) hours.

Worked example — Unbiased estimators

A sample of 5 values: 12, 15, 11, 14, 13. Find unbiased estimates of \(\mu\) and \(\sigma^2\).

\(\bar{x}=65/5=13\). \(\sum x^2=144+225+121+196+169=855\). \(s^2=\dfrac{855-5(169)}{4}=\dfrac{855-845}{4}=\dfrac{10}{4}=2.5\).

A sample of size 100 from a population (known \(\sigma=20\)) gives \(\bar{x}=142\). Find a 99% CI for \(\mu\) and state what "99% confidence" means.
\(142\pm2.576\cdot\dfrac{20}{\sqrt{100}}=142\pm5.15=(136.85,\,147.15)\). "99% confidence" means: if this process were repeated many times, 99% of the intervals produced would contain the true \(\mu\).
🔗 See also: Hypothesis Testing
S2·4

Hypothesis Testing

📌 Hypothesis Testing S2  ·  Null & alternative hypothesis  ·  Critical region  ·  One- & two-tailed tests  ·  Type I & Type II errors

Hypotheses

\(H_0\) (null hypothesis): assumed true. \(H_1\) (alternative): what we test for. One-tailed or two-tailed test.

Test Statistic

\(Z=\dfrac{\bar{X}-\mu_0}{\sigma/\sqrt{n}}\sim N(0,1)\) under \(H_0\). Compare with critical value \(z_\alpha\).

Critical Region

Range of test statistic that leads to rejection of \(H_0\). For two-tailed 5%: \(|Z|>1.96\). One-tailed 5%: \(Z>1.645\) or \(Z<-1.645\).

p-value

Probability of observing a result as extreme as the sample, assuming \(H_0\). Reject \(H_0\) if \(p\text{-value}<\alpha\).

Type I and II Errors

Type I: reject \(H_0\) when true (probability = significance level \(\alpha\)). Type II: fail to reject \(H_0\) when false (probability \(\beta\)).

Testing Poisson/Binomial

Find \(P(X\geq x_0)\) (or \(P(X\leq x_0)\)) under \(H_0\). If \(<\alpha\), reject \(H_0\). State conclusion in context.

▲ Hypothesis Testing — Reference

Steps: (1) State \(H_0\) and \(H_1\). (2) Specify significance level \(\alpha\). (3) Identify test statistic and its distribution under \(H_0\). (4) Find the critical region or \(p\)-value. (5) Compare and conclude in context.
One-tailed: \(H_1:\mu>\mu_0\) or \(\mu<\mu_0\). Two-tailed: \(H_1:\mu\neq\mu_0\) (split \(\alpha\) equally). Type I error: reject \(H_0\) when it is true (probability = \(\alpha\)). Type II error: fail to reject \(H_0\) when it is false.

Test statistic (\(\sigma\) known)
\(Z=\dfrac{\bar{X}-\mu_0}{\sigma/\sqrt{n}}\)
Critical value (5%, 1-tail)
\(z=1.645\)
Critical value (5%, 2-tail)
\(z=\pm1.96\)
Type I error prob.
\(P(\text{reject }H_0\mid H_0\text{ true})=\alpha\)
Worked example — One-tailed test for \(\mu\)

Bags of flour are labelled 500 g. A sample of 25 bags gives \(\bar{x}=497\) g. Population SD is 8 g. Test at 5% whether there is evidence that bags are underweight.

\(H_0:\mu=500\), \(H_1:\mu<500\) (one-tailed). \(Z=\dfrac{497-500}{8/5}=\dfrac{-3}{1.6}=-1.875\). Critical value: \(-1.645\). Since \(-1.875<-1.645\), reject \(H_0\). There is significant evidence at 5% that bags are underweight.

Worked example — Poisson hypothesis test

Road accidents used to occur at a rate of 4 per week. After safety measures, only 1 accident is observed in one week. Test at 5% whether the rate has decreased.

\(H_0:\lambda=4\), \(H_1:\lambda<4\). \(P(X\leq1)=e^{-4}(1+4)=5e^{-4}\approx0.0916\). Since \(0.0916>0.05\), do not reject \(H_0\). Insufficient evidence that the rate has decreased.

A manufacturer claims that the mean breaking strength of cables is at least 80 kN. A sample of 16 cables gives \(\bar{x}=77.5\) kN with population SD 5 kN. Test this claim at 1% significance.
\(H_0:\mu=80\), \(H_1:\mu<80\). \(Z=\dfrac{77.5-80}{5/4}=-\dfrac{2.5}{1.25}=-2\). Critical value at 1%: \(-2.326\). Since \(-2>-2.326\), do not reject \(H_0\). Insufficient evidence at 1% that mean breaking strength is below 80 kN.
§

Practice set

Fifty A2-style problems across functions, logarithms, trigonometry, calculus, series and vectors, tagged by difficulty. Click any problem for a full worked solution.

1

Find the inverse of \( f(x)=2x+1 \).

Basic
\[ f^{-1}(x)=\tfrac{x-1}{2}. \]
2

If \( f(x)=x^{2} \) and \( g(x)=x+1 \), find \( fg(2) \).

Intermediate

\( g(2)=3 \), then \( f(3)=9 \):

\[ 9. \]
3

Solve \( |x|=4 \).

Intermediate
\[ x=\pm4. \]
4

Solve \( |x-1|=3 \).

Advanced

\( x-1=\pm3 \):

\[ x=4,\ -2. \]
5

If \( f(x)=x^{2} \) and \( g(x)=x+1 \), find \( gf(x) \).

Intermediate

\( g(f(x))=f(x)+1 \):

\[ x^{2}+1. \]
6

State the range of \( f(x)=x^{2}+1 \).

Advanced
\[ f(x)\ge 1. \]
7

Solve \( 2^{x}=8 \).

Basic
\[ 2^{3}=8\Rightarrow x=3. \]
8

Evaluate \( \log_2 8 \).

Intermediate
\[ 3. \]
9

Evaluate \( \log_{10}1000 \).

Intermediate
\[ 3. \]
10

Solve \( e^{x}=1 \).

Advanced
\[ x=0. \]
11

Evaluate \( \ln e \).

Intermediate
\[ 1. \]
12

Solve \( \log_{10}x=2 \).

Advanced
\[ x=100. \]
13

Write \( \log a+\log b \) as a single logarithm.

Intermediate
\[ \log(ab). \]
14

Solve \( 3^{x}=81 \).

Advanced
\[ 3^{4}=81\Rightarrow x=4. \]
15

State the formula for \( \sin2\theta \).

Intermediate
\[ 2\sin\theta\cos\theta. \]
16

Evaluate \( \cos0^{\circ} \).

Intermediate
\[ 1. \]
17

Solve \( \cos\theta=0 \) for \( 0^{\circ}\le\theta\le180^{\circ} \).

Advanced
\[ \theta=90^{\circ}. \]
18

Evaluate \( \tan45^{\circ} \).

Intermediate
\[ 1. \]
19

State the exact value of \( \sin45^{\circ} \).

Advanced
\[ \tfrac{\sqrt{2}}{2}. \]
20

Express \( \sec\theta \) in terms of \( \cos\theta \).

Intermediate
\[ \sec\theta=\tfrac{1}{\cos\theta}. \]
21

Write \( \cos2\theta \) in terms of \( \cos\theta \).

Advanced
\[ 2\cos^{2}\theta-1. \]
22

State the period of \( y=\tan x \).

Intermediate
\[ 180^{\circ}. \]
23

Differentiate \( x^{4} \).

Intermediate
\[ 4x^{3}. \]
24

Differentiate \( \sin x \).

Intermediate
\[ \cos x. \]
25

Differentiate \( e^{x} \).

Intermediate
\[ e^{x}. \]
26

Differentiate \( \ln x \).

Intermediate
\[ \tfrac{1}{x}. \]
27

Differentiate \( x^{2}e^{x} \).

Advanced

Product rule:

\[ 2xe^{x}+x^{2}e^{x}=(x^{2}+2x)e^{x}. \]
28

Differentiate \( (2x+1)^{3} \).

Intermediate

Chain rule:

\[ 6(2x+1)^{2}. \]
29

Differentiate \( \cos x \).

Advanced
\[ -\sin x. \]
30

Find the gradient of \( y=x^{3} \) at \( x=2 \).

Intermediate

\( \tfrac{dy}{dx}=3x^{2}=12 \):

\[ 12. \]
31

Differentiate \( \dfrac{x}{x+1} \).

Advanced

Quotient rule:

\[ \frac{1}{(x+1)^{2}}. \]
32

Find the second derivative of \( x^{3} \).

Intermediate

\( \tfrac{dy}{dx}=3x^{2} \), again:

\[ 6x. \]
33

Find \( \displaystyle\int x^{3}\,dx \).

Intermediate
\[ \tfrac{x^{4}}{4}+C. \]
34

Find \( \displaystyle\int e^{x}\,dx \).

Intermediate
\[ e^{x}+C. \]
35

Find \( \displaystyle\int \cos x\,dx \).

Intermediate
\[ \sin x+C. \]
36

Find \( \displaystyle\int \tfrac{1}{x}\,dx \).

Advanced
\[ \ln|x|+C. \]
37

Evaluate \( \displaystyle\int_{0}^{1} x\,dx \).

Intermediate
\[ \left[\tfrac{x^{2}}{2}\right]_{0}^{1}=\tfrac12. \]
38

Evaluate \( \displaystyle\int_{0}^{\pi} \sin x\,dx \).

Advanced
\[ \left[-\cos x\right]_{0}^{\pi}=2. \]
39

Find \( \displaystyle\int 6x^{2}\,dx \).

Intermediate
\[ 2x^{3}+C. \]
40

Find the area under \( y=x^{2} \) from \( 0 \) to \( 3 \).

Advanced
\[ \left[\tfrac{x^{3}}{3}\right]_{0}^{3}=9. \]
41

State the sum of the first \( n \) integers.

Intermediate
\[ \tfrac{n(n+1)}{2}. \]
42

Find the 10th term of the AP \( 2,5,8,\dots \)

Intermediate

\( a=2,\ d=3 \):

\[ 2+9(3)=29. \]
43

Find the 5th term of the GP \( 3,6,12,\dots \)

Advanced

\( a=3,\ r=2 \):

\[ 3\cdot2^{4}=48. \]
44

Expand \( (1+x)^{2} \).

Intermediate
\[ 1+2x+x^{2}. \]
45

Find the sum \( 1+2+\dots+100 \).

Advanced
\[ \tfrac{100\cdot101}{2}=5050. \]
46

Find the sum to infinity of a GP with \( a=1 \), \( r=\tfrac12 \).

Intermediate
\[ \frac{1}{1-\tfrac12}=2. \]
47

Find the magnitude of \( (3,4) \).

Intermediate
\[ \sqrt{9+16}=5. \]
48

Find \( (1,2)+(3,1) \).

Intermediate
\[ (4,\,3). \]
49

Find \( 2(1,3) \).

Advanced
\[ (2,\,6). \]
50

Find the magnitude of \( (6,8) \).

Intermediate
\[ \sqrt{36+64}=10. \]

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Based on Cambridge International A Level Mathematics 9709 Paper 3: Pure Mathematics 3. Advanced topics: complex numbers, series, differential equations, vectors, numerical methods.

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