When θ \theta\,θ is small, cos2θsinθ\displaystyle \frac{\cos 2\theta}{\sin \theta}sinθcos2θ can be approximated by 1−2θ2θ\displaystyle \frac{1 - 2\theta^2}{\theta}θ1−2θ2.
Hence, approximate the value of cosπ10sinπ20\displaystyle \frac{\cos \frac{\pi}{10}}{\sin \frac{\pi}{20}}sin20πcos10π
278 exam-style questions on Edexcel A Level Maths Radians, covering 5.1 Radian Measure, 5.2 Arc Length, 5.3 Areas of Sectors and Segments, 5.4 Solving Trigonometric Equations, and 5.5 Small Angle Approximations. Each one has a worked solution and a mark scheme showing where the marks go.