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A Level · Cambridge (CIE) · 9709

Find every trigonometric solution in a stated interval

Use reference angles and periodic graphs, enlarge the interval for a multiplied argument and check endpoints before listing solutions.

Pure Mathematics 1 · Trigonometry · 1.5

Pure Mathematics 1 (Paper 1) · AS & A Level Mathematics 9709, 2026–2027. State angle units and find every solution in the supplied interval; general forms of solution are not required in section 1.5. Written practice is self-checked.

Before you begin

  • Use principal inverse values and trigonometric graph periods.
  • Solve inequalities for a transformed angle and interpret open or closed endpoints.

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

Quick readiness check

If 0 ≤ x ≤ π and u = 2x, what is the interval for u?

What you will learn

  • Find all simple sine, cosine and tangent equation solutions within a supplied interval.
  • Transform the full argument interval before solving an equation containing a multiplied angle.

Use the interval and the graph to complete the answer

For sin x = 1/2 on 0° ≤ x ≤ 360°, the reference angle is 30°. Sine is positive in quadrants I and II, so x = 30° or 150°. For cosine use its horizontal-coordinate sign, and for tangent use the sine/cosine quotient sign with period 180°. For tan x = −1 on −180° < x ≤ 180°, the complete answer is −45° or 135°.

Check interval endpoints explicitly. sin x = 0 on 0° ≤ x ≤ 360° has solutions 0°, 180° and 360°; replacing the final ≤ by < removes 360°. Do not combine equivalent directions if they are distinct numbers in the requested interval. Values such as sin x = 1.1 have no real solutions; an inverse-key error is then evidence of an impossible ratio.

Solve in the argument's full interval, then undo the change

For cos 2x = 1/2 with 0 ≤ x ≤ π, put u = 2x, so 0 ≤ u ≤ 2π. Within this enlarged interval, u = π/3 or 5π/3. Divide both values by 2 to obtain x = π/6 or 5π/6. Solving only for one principal u loses a valid answer; solving over the original x interval as if it belonged to u can also lose answers.

For sin 2x = −1/2 with 0° ≤ x < 360°, the argument covers 0° ≤ u < 720°, so it contains two full sine periods. List the four negative-sine arguments 210°, 330°, 570° and 690° before halving them. If there is an input shift, transform both interval endpoints too. This section requests solutions in specified intervals, so a general infinite solution formula is unnecessary.

Pause and explain

Solve sin x = 0 on 0° ≤ x ≤ 360°.

Put the idea to work

Worked example

Solve cos 2x = 1/2 for 0 ≤ x ≤ π.

Show the worked solution
  1. Let u = 2x and transform the interval to 0 ≤ u ≤ 2π.
  2. Cosine is positive at the π/3 reference angle in quadrants I and IV, so u = π/3 or 5π/3.
  3. Divide each by 2, check the original interval and substitute to verify both.

Answer x = π/6 or 5π/6.

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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

Solve cos x = −√2/2 for 0 ≤ x < 2π.

Give me a hint

Use a π/4 reference angle and the quadrants with negative cosine.

Compare my reasoning
  1. The exact magnitude √2/2 gives reference angle π/4.
  2. Negative cosine occurs in quadrants II and III, giving x = π − π/4 = 3π/4 and x = π + π/4 = 5π/4.
  3. Both values are in the interval and give the required ratio; neither endpoint is a solution.

x = 3π/4 or 5π/4.

Look for these in your work

  • Choose both quadrants for the required sign.
  • Check the interval and original ratio.
2 · Independent

Solve sin 2x = −1/2 for 0° ≤ x < 360°.

Give me a hint

Use u = 2x and find all negative-sine values over two full turns.

Compare my reasoning
  1. The argument interval is 0° ≤ u < 720°.
  2. The solutions for u are 210°, 330°, 570° and 690°.
  3. Halve every value to obtain x = 105°, 165°, 285° and 345°; all satisfy the original interval.

x = 105°, 165°, 285° or 345°.

Look for these in your work

  • Expand the argument interval before using periodicity.
  • Retain every solution when dividing back to x.
3 · Transfer

A supplied model is h(t) = 2 + 3 sin(πt/6) metres for 0 ≤ t ≤ 12 seconds. Find every time when h = 3.5 metres.

Give me a hint

Isolate the sine value, then transform the time interval into an angle interval.

Compare my reasoning
  1. Set 2 + 3 sin(πt/6) = 3.5 to obtain sin(πt/6) = 1/2.
  2. For u = πt/6, the time interval gives 0 ≤ u ≤ 2π, with solutions u = π/6 and 5π/6.
  3. Use t = 6u/π to get 1 and 5 seconds; substitute each in the original height model.

t = 1 s or 5 s.

Look for these in your work

  • Isolate the ratio without confusing the height with the sine output.
  • Convert all permitted angles back into times with units.

Common mistakes

  • The principal inverse value is only a starting angle.
  • Transform the whole interval when the argument is multiplied or shifted.
  • Check open endpoints, closed endpoints and excluded tangent inputs.
Recall without your notes

What can you explain now?

Solve sin x = 0 for 0° ≤ x ≤ 360°.

Compare with the explanation

x = 0°, 180° or 360°.

The graph has zeros at both included endpoints as well as at the half turn.

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

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Make it stick

Explain why sin 2x can have four answers over one full turn of x. Describe the interval change and endpoint check before any inverse calculation.

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

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.

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