A Level · Cambridge (CIE) · 9709

Use a given substitution and transform every integration limit

Rewrite the differential and all remaining factors in the new variable, change definite limits, and return to the original variable for an indefinite answer.

Pure Mathematics 3 · Integration · 3.5

Exam scope and assessment notes

Pure Mathematics 3 (Paper 3, A Level) · Mathematics 9709, 2026–2027, section 3.5. Paper 1 integration, shared standard integrals and identities, Paper 3 partial fractions and derivatives are assumed. Rational decompositions follow the three denominator forms in section 3.1; higher-degree numerators are excluded, while equal-degree cases may need division first. Substitution questions use a given substitution. Trigonometric and inverse-tangent outputs use radians. Written practice is self-checked; human subject-teacher review remains pending.

Before you begin

Differentiate composites and use double-angle identities.
Integrate powers and exponentials and evaluate endpoints in a single variable.

Work on paper. Try each question before revealing help, and explain why your method works.

Quick readiness check

For u = sin x with radian input, what is du?

What you will learn

Use a supplied substitution to simplify definite and indefinite integrals.
Transform both endpoints and the entire integrand without mixing variables or reversing the orientation unnoticed.

This schematic tracks the given substitution u = sin x for the integral of sin²(2x)cos x from x = 0 to x = π/6. The top box contains the original x endpoints. The first arrow maps them to u = 0 and u = 1/2. The second arrow uses du = cos x dx and sin²(2x) = 4u²(1 − u²). The bottom box contains the transformed u integral. Its primitive evaluated at the u endpoints gives 17/120. The boxes are a process diagram, not a graph or a scale comparison; no x limits remain on the u integral.

A substitution rewrites the whole differential expression

If a problem gives u = g(x), differentiate to obtain du = g′(x) dx and use it to replace the matching differential factor. Express every remaining factor in u as well. For ∫sin²(2x)cos x dx with the given u = sin x, du = cos x dx. Since sin(2x) = 2sin x cos x and cos²x = 1 − sin²x, sin²(2x) becomes 4u²(1 − u²). The transformed integral is 4∫(u² − u⁴) du, with no x left in it.

The primitive in u is 4u³/3 − 4u⁵/5 + C. For an indefinite integral, replace u by sin x to give 4sin³x/3 − 4sin⁵x/5 + C. Differentiation returns 4sin²x cos³x = sin²(2x)cos x, so the identity and differential conversion are independently checked. The syllabus asks you to use a given substitution; choosing an unsupported substitution is not needed for this objective.

Definite limits belong to the variable of integration

On x from 0 to π/6, the substitution u = sin x changes the limits to 0 and 1/2. The transformed integral is 4∫ from 0 to 1/2 of (u² − u⁴) du. Evaluating gives 1/6 − 1/40 = 17/120. Do not keep the radian x limit π/6 on a u integral. Alternatively, back-substitute the primitive and then evaluate the original x endpoints; either method uses one consistent variable at a time.

For a given u = 1 + x², du = 2x dx, so ∫ from 0 to 1 of 2x/(1 + x²)² dx becomes ∫ from 1 to 2 of u^(−2) du = 1/2. A decreasing substitution may reverse the endpoint order; keep the derivative sign and transformed orientation together rather than discarding both independently. If an inverse expression is needed for x or a square root, use the original interval to choose its valid branch. A missing derivative factor cannot simply disappear.

Pause and explain

After substituting u = sin x in an integral from x = 0 to x = π/6, which limits go with du?

Put the idea to work

Worked example

Use the given substitution u = sin x to integrate sin²(2x)cos x, then evaluate from 0 to π/6.

Show the worked solution

Set du = cos x dx and rewrite sin²(2x) as 4u²(1 − u²).
Integrate to get 4u³/3 − 4u⁵/5 + C, or back-substitute for an indefinite answer.
For the definite integral use u limits 0 and 1/2, giving 1/6 − 1/40 = 17/120.

Answer Primitive 4sin³x/3 − 4sin⁵x/5 + C; definite integral 17/120.

Try a topic test

Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.

Test this topic →

From guided practice to a new situation

Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.

1 · Guided

Using the given u = 1 + x², evaluate ∫ from 0 to 1 of 2x/(1 + x²)² dx.

Give me a hint

The numerator times dx is exactly du; transform both bounds.

Compare my reasoning

Since du = 2x dx, the integrand becomes u^(−2) du.
The bounds become u = 1 and u = 2.
The primitive −1/u gives −1/2 − (−1) = 1/2.

1/2.

Look for these in your work

Transform the differential and both limits.
Apply the negative-power rule with the correct sign.

2 · Independent

Use the given u = x² + 3 to evaluate ∫ from 1 to 2 of x√(x² + 3) dx, and give its primitive in x.

Give me a hint

Use x dx = du/2 and change bounds to the values of x² + 3.

Compare my reasoning

The transformed definite integral is (1/2)∫ from 4 to 7 of u^(1/2) du.
Its primitive is u^(3/2)/3, so the result is (7√7 − 8)/3.
Back-substitution gives primitive (x² + 3)^(3/2)/3 + C, whose derivative is x√(x² + 3).

Definite integral (7√7 − 8)/3; primitive (x² + 3)^(3/2)/3 + C.

Look for these in your work

Retain the factor 1/2 from the differential.
Use one variable at a time and verify the back-substituted primitive.

3 · Transfer

A vessel starts with 4 litres and has supplied inflow q(t) = t e^(t²) litres per minute for 0 ≤ t ≤ √(ln 2), with t measured numerically in minutes. Use the given u = t² to find added volume and final total.

Give me a hint

The differential t dt is du/2; the final transformed endpoint is ln 2.

Compare my reasoning

With du = 2t dt, the accumulated volume is (1/2)∫ from 0 to ln 2 of eᵘ du.
Evaluation gives (1/2)(2 − 1) = 1/2 litre added.
Adding the original 4 litres gives final total 9/2 = 4.5 litres.

Added volume 1/2 litre; final total 9/2 = 4.5 litres.

Look for these in your work

Include the differential factor and transform the stated endpoint.
Interpret the rate's accumulation before adding the initial stock.

Common mistakes

Rewrite every factor and the differential, rather than only renaming the denominator.
Use u endpoints for a u integral, or back-substitute before using x endpoints.
For an indefinite answer return to the original variable and keep C.

Recall without your notes

What can you explain now?

With u = 1 + x², what are the transformed limits for x from 0 to 1?

Compare with the explanation

u from 1 to 2.

Evaluate the given substitution at both original endpoints.

After trying it yourself, choose your next review. This is your self-assessment.

Your review choice appears on Today. Sign in to sync it across devices.

Continue to next lesson Back to Today

Make it stick

For a given substitution, record its derivative, rewrite every factor and transform both definite limits. Explain why mixed variables or mixed limits cannot be used in the same integral.

If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.

Keep learning Mathematics

Check the official syllabus 2026–2027

Course scope and assessment

312 sequenced lessons provide 936 guided, independent and application problems covering the 160 objectives in sections 1.1–1.8, 2.1–2.6, 3.1–3.9, 4.1–4.5, 5.1–5.5 and 6.1–6.5. The map lists all 38 sections across six alternative components; all eight Pure Mathematics 1 sections and all six Pure Mathematics 2 sections, from Paper 2 Algebra through Numerical solution of equations, currently have full teaching sequences. Paper 3 Algebra, section 3.1, links the six shared foundation lessons plus six lessons on partial fractions and rational binomial expansions; Paper 3 logarithms, trigonometry and numerical equations use the shared lessons, with the Paper 1 graph foundation linked into trigonometry. Paper 3 differentiation combines the shared methods with its inverse-tangent derivative lesson. Paper 3 Integration links four shared standard and identity lessons plus seven advanced lessons, covering all six section 3.5 requirements. Eight Vectors lessons cover all six section 3.7 requirements, with 2D and 3D line and solid applications. Nine Differential equations lessons cover all four section 3.8 requirements, including Paper 3 integration techniques, initial conditions, equilibrium solutions and conditional model interpretations. Eleven Complex numbers lessons cover all eight section 3.9 requirements, with seven Argand diagrams and explicit argument and boundary checks. All nine Pure Mathematics 3 sections now have teaching linked to every mapped requirement. Nine Forces and equilibrium lessons cover all seven section 4.1 requirements, with six force diagrams, signed incline-friction intervals, reaction-dependent pull and push limits and separate-body third-law checks. Nine Kinematics lessons cover the four official section 4.2 requirements, with the graph requirement mapped to three relationships. Six motion diagrams support directed quantities, graph slopes and signed areas, Paper 1 time-calculus methods, reversal distances, constant-acceleration stages and shared-clock particle meetings. Six Momentum lessons cover both section 4.3 requirements, including signed system totals, conservation assumptions, outgoing velocities, coalescence, unknown masses and successive impacts. Four diagrams show system momentum through the stipulated events, and supplied kinetic-energy checks distinguish conservation of momentum from changes in kinetic energy. Twelve Newton’s laws lessons cover all four section 4.4 requirements, with vertical support and release stages, rough horizontal and incline motion, inferred parameters, hanging and surface pulley systems, rigid tow-bar thrust and slack-string transitions. Seven force diagrams support the separate-particle balances. Nine Energy, work and power lessons cover all five section 4.5 requirements, with angle-dependent work, kinetic and reference potential energy, signed net-work balances, smooth curved slides, rough and driven slopes, ideal connected-system energy and instantaneous power on hills. Five diagrams distinguish the energy inputs, losses and valid positive-speed force model. All five Mechanics sections now have teaching and staged practice linked to their mapped requirements. Thirteen Representation of data lessons cover all five section 5.1 requirements, including choice and limitations of displays, ordered and back-to-back stems, raw summaries and box plots, unequal-width density histograms, cumulative-frequency interpolation, descriptive moment calculations, grouped estimates, coding, combining two datasets and correcting totals. Six accessible diagrams retain repeated observations and distinguish numerical spread, frequency area and estimated readings. Ten Permutations and combinations lessons cover both official section 5.2 requirements, with selection and ordered roles, repeated objects, adjacency blocks, non-adjacency gaps, leading-zero cases, labelled multi-row seating and mixed restrictions. Six accessible diagrams show outcome trees, ordered versus unordered choices, repeated copies, blocks, gaps and distinct row seats. Eleven Probability lessons cover all four section 5.3 requirements, with equiprobable elementary outcomes, selection-based probabilities, complements and disjoint regions, independence tests, restricted sample spaces, two-way tables, replacement and removal trees, reversed conditions and unknown parameters. Seven accessible diagrams show dice outcomes, random subsets, event regions, a conditioned grid, a count table and two probability trees. Twelve Discrete random variables lessons cover all three official section 5.4 requirements, with complete probability tables, moment and parameter checks, binomial assumptions, exact probabilities and moments, geometric first-success probabilities, tails, expectation and integer reliability thresholds. Six accessible diagrams distinguish outcome grouping, weighted moments, fixed trials, discrete probability bars, waiting conventions and integer tail deadlines. Twelve Normal distribution lessons cover all three official section 5.5 requirements, with continuous-area interpretation, MF19 cumulative tables, full standardisation, tail and interval regions, conditional probabilities, percentiles, one- and two-parameter inference, binomial suitability, continuity corrections and approximate integer thresholds. Seven accessible diagrams show model areas, table reading, aligned scales, intervals, quantiles, matched binomial and normal shapes and whole integer cells. All five Statistics 1 sections now have teaching and staged practice linked to their mapped requirements. Fourteen Poisson distribution lessons cover all five official section 6.1 requirements, with homogeneous event-count assumptions, exposure scaling, exact masses and tails, conditional count events, moments, parameter inference, probability duration targets, disjoint and overlapping windows, rare-count binomial approximations, matched normal approximations and continuity corrections. Nine accessible diagrams show event exposures, unit conversions, discrete bars, complete tail complements, population moments, shared windows, approximate count models and integer cells. Exact checks distinguish approximate and exact close-target decisions. Fourteen Linear combinations lessons cover the six listed results in official section 6.2, with affine moments, signed scales and constant cases, expectation without independence, independent squared variance contributions, fixed and random fees, independent copies versus reused values, affine normal events, independent normal sums and differences, weighted and conditional areas, coefficient inference, exact independent Poisson sums and overlapping exposure limits. Nine accessible diagrams distinguish scale changes, variance contributions, component costs, copy mechanisms, aligned normal scales, summed areas, Poisson count pairs and unsupported distribution claims. Fourteen Continuous random variables lessons cover both official section 6.3 requirements, with density validity and units, support-aware intervals, complements and conditional regions, first and second moments, percentiles by direct density areas, symmetry checks, parameter inference, infinite-support power and exponential integrals, divergent-moment limits and combined applications. Nine accessible diagrams distinguish density height from probability, normalisation, negative-density failures, central and conditional areas, mean versus median, percentile locations and partial infinite tails. Explicit cumulative distribution function knowledge is not required. Eighteen Sampling and estimation lessons cover all eight official section 6.4 requirements, with population and frame definitions, random-number selection, sampling-quality limits, independent sample-mean moments, normal means, CLT conditions, SE scaling, raw, summarised and coded unbiased estimates, known-variance and large-sample mean intervals, repeated-sampling interpretation, precision planning, proportion intervals, sparse-outcome limits and contextual applications. Ten accessible diagrams distinguish selection frames, number rejection, repeated sample means, population versus mean density, CLT models, variance divisors, interval targets, illustrative coverage, integer size checks and proportion margins. Eighteen Hypothesis tests lessons cover all five official section 6.5 requirements, with pre-specified alternatives, inclusive count tails, explicit equal-tail conventions, integer critical regions and actual significance, exposure-aware Poisson tests, continuity-corrected count approximations, normal and large-sample mean tests, confidence-interval connections, error classifications, fixed-region binomial, Poisson and normal error probabilities and sample-size power comparisons. Nine accessible diagrams show the testing procedure, exact count regions, unequal Poisson tails, discrete significance jumps, corrected count boundaries, matching mean intervals and alternative error distributions. All shared lessons are counted once in the course total. All 38 sections now link teaching and practice. Eight earlier overview lessons remain available, but do not count as full section coverage. This is a content-availability measure, not full programme completion or exam readiness. Written practice is self-checked, not officially marked. Check the 2028–2030 syllabus separately if sitting an examination from 2028; this teaching map uses 2026–2027 requirements.