Figure 1 below shows the right-angled triangle ABCABCABC, in which the angle at C C\,C is a right angle and AB=5AB = 5AB=5 cm.
The angle BAC BAC\,BAC is θ\thetaθ, where θ \theta\,θ is measured in radians.
Given that θ \theta\,θ is small, show that AC≈5−5θ22\displaystyle AC \approx 5 - \frac{5\theta^2}{2}AC≈5−25θ2.
Hence find the length of AC AC\,AC when θ=0.1\theta = 0.1θ=0.1, giving your answer to four decimal places.
317 exam-style questions on AQA A Level Maths 1.8 E: Trigonometry, covering 1.8.1 Trigonometric definitions, rules and radians, 1.8.2 Small angle approximations (A-level only), 1.8.3 Trigonometric functions and exact values, 1.8.4 Reciprocal and inverse trigonometric functions (A-level only), 1.8.5 Trigonometric identities, 1.8.6 Compound and double angle formulae (A-level only), 1.8.7 Solving trigonometric equations, 1.8.8 Proofs with trigonometric identities, and 1.8.9 Trigonometry in context. Each one has a worked solution and a mark scheme showing where the marks go.