How to understand:
1. The use of trigonometric ratios (sine, cosine and tangent) of acute angles to calculate unknown sides and angles in right-angled triangles.
2. Extending sine and cosine to obtuse angles.
3. Use of the formula ½ ab sinC for the area of a triangle.
4. Use of sine rule and cosine rule for any triangle.
5. Problems in 2 and 3 dimensions including those involving angles of elevation and depression and bearings. (Exclude calculation of the angle between two planes or of the angle between a straight line and a plane).