National 5; Using the sine and cosine rules to find a side or angle in a triangle The sine rule. The sine rule can be used to find an angle from 3 sides and an angle, or a side from 3 angles and a ...

Trigonometry - Edexcel The sine rule - Higher. The three trigonometric ratios; sine, cosine and tangent are used to calculate angles and lengths in right-angled triangles.

By using the Law of Sines, and avoiding the Pythagorean theorem’s trig identity (sin²α + cos²α = 1), Johnson and Jackson successfully proved the theorem without resorting to circular reasoning.