Trigonometry is Pure Topic 5 in the Edexcel A level Mathematics specification (9MA0), spanning both years. Year 1 covers the sine and cosine rules, the shapes of sin, cos and tan graphs, exact values in degrees, the two basic identities, and solving trig equations over an interval. Year 2 adds radians, arc length and sector area, small-angle approximations, reciprocal and inverse trig functions, the second identity pair, compound and double-angle formulae, R-form, formal proofs, and trig modelling. Across the three papers it typically accounts for around 28 of the 300 available marks — an estimate.
The topic splits sharply between what the formula booklet gives and what you must memorise: the sine rule, cosine rule, area formula and both identity pairs are memory items, while the compound-angle formulae and small-angle approximations are printed. Arc length and sector area sit in between — everyday formulae that Edexcel never prints, so they still need to be learned.
The specification statements this topic covers. AS = Year-1 content, also assessed in the standalone AS course (8MA0); A2 = full A level only. Typical share of a 300-mark series: ≈28 marks — our estimate from the 2018–2025 papers, not an official weighting.
| Ref | Spec statement | Level |
|---|---|---|
| 5.1 | Sine and cosine rules | AS |
| 5.1 | Radians, arcs and sectors | A2 |
| 5.2 | Small angle approximations | A2 |
| 5.3 | Trig graphs and exact values | AS |
| 5.4 | Reciprocal and inverse trig functions | A2 |
| 5.5 | tan = sin/cos and sin² + cos² = 1 | AS |
| 5.5 | sec² = 1 + tan² and cosec² = 1 + cot² | A2 |
| 5.6 | Compound/double angles and R-form | A2 |
| 5.7 | Solving trig equations | AS |
| 5.8 | Proving trig identities | A2 |
| 5.9 | Trig in context | A2 |
Examiners repeatedly report that identity proofs lose marks when a step is skipped or the argument works backwards from the printed result. Build each line from one side of the identity, not both sides at once — later parts of a question use the printed result even if your own working differed.
A correctly rounded decimal earns nothing when a question asks for an exact value — surd or π-based form is what's tested. The same shows up in modelling: finding a model's constants isn't the same as writing its complete equation, which candidates often omit.
Trig equations are usually meant to be solved algebraically, and forming the equation correctly often carries marks of its own. An answer read straight off a calculator, with no supporting working, scores little wherever the question rules out calculator-only methods.
A trig graph 'sketch' is marked on shape and key features — intercepts, period, amplitude, and asymptotes for tan, sec or cosec — not on being to scale. Examiners flag graphs too rough to show the right features, or over-laboured beyond the marks available.
Finding an angle from sin A = k usually gives two possibilities between 0° and 180° — A itself and its supplement. Check both against the angle sum unless the triangle rules one out.
Arc length, sector area, small-angle approximations and trig calculus only hold in radians. Confirm the angle unit before applying s = rθ or A = ½r²θ, and check the calculator mode matches it.
It's easy to find one root and stop, or forget that solving for 2x or ½x stretches the interval you must search. Sketch the graph over the full range and count the crossings expected.
Writing a cos θ + b sin θ as R cos(θ − α) goes wrong when tan α is inverted, α sits in the wrong quadrant, or R is left as a² + b² unrooted. Expand the R-form and match coefficients to check all three.
It's a common slip to write sec²θ = tan²θ − 1, or pair cosec² with tan² instead of cot². Both come from dividing sin²θ + cos²θ = 1 by cos²θ or sin²θ — deriving the one needed beats recalling it under pressure.
We haven’t published checked questions for this topic yet — a worked sample appears here only once a question has passed every check. In the meantime you can practise in the app.
Separate what must be memorised from what the booklet supplies: the sine and cosine rules, the area formula, both identity pairs, and the double-angle formulae need to be secure from memory, while the compound-angle formulae and small-angle approximations can be looked up. Arc length and sector area fall outside the booklet entirely, so they're worth drilling deliberately.
Check your calculator's angle mode before every trig calculation, and practise switching between degrees and radians as a question demands rather than fixing one for a whole session — mixing modes under pressure is one of the most avoidable ways to lose marks here.
Practise equation-solving and identity proofs without leaning on a calculator's equation solver, since the algebraic route is usually what's assessed. Mix Year 1 triangle and graph questions with Year 2 identity and modelling questions — a good share of marks in this topic come from combining two or three techniques in one question, such as a double-angle formula before solving over a given interval.
All 19 topics: Edexcel A level Maths topic guides. Reference: formula booklet vs memorise and grade boundaries.
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Original questions written for the Pearson Edexcel A Level Mathematics (9MA0) specification. Not affiliated with or endorsed by Pearson.