A Level · Cambridge (CIE) · 9709

Find total areas by splitting at axis crossings

Locate sign changes, integrate on each interval and add positive magnitudes for a geometric area or total distance.

Section 1.8 · Integration

Pure Mathematics 1 · Integration · 1.8

Pure Mathematics 1 (Paper 1) · AS & A Level Mathematics 9709, 2026–2027. Section 1.8 includes rational and linear-composite powers except exponent −1, simple improper integrals, areas and volumes about either coordinate axis, including regions away from the rotation axis. Written practice is self-checked.

Before you begin

Solve a polynomial's zero equation and determine its signs.
Evaluate definite integrals and interpret signed accumulation.

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

Quick readiness check

Where does y = x² − 1 cross the x-axis?

What you will learn

Find the area between a curve, an axis and lines parallel to the axes.
Split at crossings so total area or distance does not cancel.

The curve y = x² − 1 crosses the x-axis at −1 and 1. From −2 to 2, the blue regions above the axis each have area 4/3, and the red region below the axis has area 4/3. Their signed contributions are 4/3, −4/3 and 4/3, so the net integral is 4/3 while the total geometric area is 4 square units. The axes use different drawing scales; the labelled values, rather than drawn areas, give the exact quantities.

Locate every relevant axis crossing before integrating

A geometric area is non-negative. Above the x-axis, the vertical height is y; below it, the height from the curve to the axis is −y. On a finite interval, solve y = 0 and split at each root inside the stated bounds where the sign can change. Integrate the positive height on each part or take the magnitude of each signed part. Taking the absolute value of a single net integral can still undercount an area with cancelling contributions.

For y = x² − 1 from x = −2 to 2, the roots are −1 and 1. The graph is above the axis on [−2, −1] and [1, 2], and below it on [−1, 1]. With F(x) = x³/3 − x, the three signed integrals are 4/3, −4/3 and 4/3. The total area is 4/3 + 4/3 + 4/3 = 4 square units, while the single signed integral is 4/3.

Choose height and units to match the request

For a curve wholly below the axis, integrate 0 − y rather than report a negative area. For y = −x² between x = 0 and 2, the signed integral is −8/3 but the geometric area is 8/3 square units. Bounds may be stated as vertical or horizontal lines; use a variable in which each strip has a clearly specified positive width or height, with the matching differential.

Signed velocity behaves the same way. For v(t) = 2t − 4 on 0 ≤ t ≤ 3, the direction changes at t = 2. The distance is −∫₀²(2t − 4) dt + ∫₂³(2t − 4) dt = 4 + 1 = 5 m. The displacement remains −3 m. An area in a velocity–time graph has distance units because (m/s) × s = m, rather than square metres.

Pause and explain

Three signed area pieces are 4/3, −4/3 and 4/3. What is their total geometric area?

Put the idea to work

Worked example

Find the total area between y = x² − 1 and the x-axis for −2 ≤ x ≤ 2, and compare the signed integral.

Show the worked solution

Solve x² − 1 = 0: split at x = −1 and 1, with signs positive, negative and positive.
Using F(x) = x³/3 − x gives signed pieces 4/3, −4/3 and 4/3.
Add their magnitudes for total area 4; their signed sum is 4/3.

Answer Total area 4 square units; signed integral 4/3.

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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

Find the area between y = 2x − 2 and the x-axis on 0 ≤ x ≤ 3, then compare its signed integral.

Give me a hint

Split at x = 1 and use F(x) = x² − 2x.

Compare my reasoning

The graph is below the axis on [0, 1] and above it on [1, 3].
The signed pieces are F(1) − F(0) = −1 and F(3) − F(1) = 4.
The total area is 1 + 4 = 5 square units; the net integral is −1 + 4 = 3.

Total area 5 square units; signed integral 3.

Look for these in your work

Split at the root within the bounds.
Add magnitudes for total area and signs for the net integral.

2 · Independent

Find the area enclosed by y = x(3 − x) and the x-axis.

Give me a hint

Find both roots and check which side of the axis contains the enclosed region.

Compare my reasoning

The roots are x = 0 and 3; the parabola is non-negative between them.
The area is ∫₀³(3x − x²) dx = [(3/2)x² − x³/3]₀³.
Evaluation gives 27/2 − 9 = 9/2 square units, with no sign split inside the interval.

Area 9/2 square units.

Look for these in your work

Use both intersections to determine the enclosed bounds.
Check the sign before treating an integral as an area.

3 · Transfer

For signed velocity v(t) = 2t − 4 m/s on 0 ≤ t ≤ 3, find both total distance and displacement.

Give me a hint

Split at the direction change t = 2 for distance, while displacement uses signed contributions.

Compare my reasoning

The zero velocity occurs at t = 2; the signed integral from 0 to 2 is −4 m.
From 2 to 3 the signed integral is 1 m, so total distance is 4 + 1 = 5 m.
Displacement is −4 + 1 = −3 m, describing the net position change.

Distance 5 m; displacement −3 m.

Look for these in your work

Reverse the negative contribution for distance.
Keep signed contributions for displacement and state metres.

Common mistakes

The absolute value of the net integral is not generally total area.
Use every sign-changing root inside the bounds.
Read the axes' units before assigning area or distance units.

Recall without your notes

What can you explain now?

For y = −x² on 0 ≤ x ≤ 2, give the signed integral and the geometric area.

Compare with the explanation

Signed integral −8/3; geometric area 8/3 square units.

The curve is below the axis throughout; integrate −y or take the magnitude of this one signed part.

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Make it stick

Given a curve crossing an axis, explain why sign splits must precede a total-area calculation. Use the same reasoning to distinguish distance and displacement.

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.