IB Math AI HL · Topic 5
Calculus
At SL calculus is applied to polynomials: optimisation and area. At HL it is deeper and wider — the chain, product and quotient rules, integration by substitution, volumes of revolution — and then it opens onto differential equations: separating variables, slope fields, Euler's method and coupled systems whose behaviour is read from eigenvalues.
What the syllabus covers
Eighteen assessed sections: SL 5.1 to 5.8, shared with AI SL, and AHL 5.9 to 5.18, which are HL only.
How it is examined
Calculus at HL is examined as technique and as modelling. The technique is by hand where an exact answer is asked for.
From AHL 5.9 differentiation and integration go beyond polynomials: rational powers, sin, cos, tan, eˣ and ln x, done by hand. The GDC verifies; it does not replace the working when an exact answer is asked for.
Related rates connect a relationship to time: write the relationship, differentiate with respect to t, substitute. Units and the sign of the rate — increasing or decreasing — belong to the answer.
A point of inflexion needs a change of concavity, not just f″(x) = 0. The sign of f″ either side is the justification.
A volume of revolution is π∫y² dx about the x-axis, and π∫x² dy about the y-axis. Which variable you integrate with respect to, and the limits in that variable, are most of the working.
A differential equation from a context is built from a sentence: write dy/dx, separate, integrate both sides, and use the initial condition to find the constant.
Euler's method is a written table. Each step uses the previous values: xₙ₊₁ = xₙ + h and yₙ₊₁ = yₙ + h f(xₙ, yₙ). For a coupled system, both components are updated from the old values.
For coupled linear systems the equilibrium is where both derivatives are zero, and its type is read from the eigenvalues of the system's matrix.
A marked question, mark by mark
An Euler's-method question where the steps are right and the percentage error is measured against the wrong value.
Practise the whole chain, on fresh exercises
From SL 5.1 to AHL 5.18, every generated exercise comes back mark by mark, with a reason for each — so a quietly shifted step in Euler's method shows up now, not on results day.
Start your trialNew to the codes? M1, A1, R1 explained →
Euler's method · AHL 5.16
Seed 1V63
Consider dy/dx = x + y with y(0) = 1. Use Euler's method with step h = 0.1 to estimate y(0.2). The exact value is y(0.2) = 1.24281, to five decimal places.
- (a)Find the Euler estimate of y(0.2).
- (b)Find the percentage error of the estimate, correct to three significant figures.
Your work
y₁ = 1 + 0.1(0 + 1) = 1.1
y₂ = 1.1 + 0.1(0.1 + 1.1) = 1.22
error = (1.24281 − 1.22) / 1.22 × 100 = 1.87%
Marks awarded
- M1Mark awarded. Euler's formula applied with the previous x and y values at each step.
- A1Mark awarded. y(0.2) ≈ 1.22.
- A1Mark not awarded. The error was divided by the estimate, 1.22. A percentage error is relative to the exact value: 0.02281 / 1.24281 = 1.84%.
Where marks are actually lost
At HL the working is longer, and the marks are lost where one line of it quietly changes.
Dividing by the approximation instead of the exact value when finding a percentage error.
CostThe percentage is for a different quantity. The method mark may stay; the accuracy mark does not.
Using the new x, or the wrong step, inside the slope in an Euler step.
CostEuler's method evaluates the slope at the start of each step. A shifted value changes every later line.
Calling a point an inflexion because f″(x) = 0.
CostA zero of the second derivative is only a candidate. The reasoning mark is for the change of concavity either side.
Dropping the constant of integration after separating the variables.
CostThe general solution is incomplete, so there is nothing for the initial condition to fix, and the marks that follow are lost.
Other Math AI HL topics
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