ABSTRACT
This chapter states and uses the sine rule and the cosine rule. It uses various formulae to determine the area of any triangle and applies the sine and cosine rules to solving practical trigonometric problems. To ‘solve a triangle’ means ‘to find the values of unknown sides and angles’. If a triangle is right-angled, trigonometric ratios and the theorem of Pythagoras may be used for its solution. However, for a non-right-angled triangle, trigonometric ratios and Pythagoras' theorem cannot be used. Instead, two rules, called the sine rule and cosine rule, are used. There are a number of practical situations where the use of trigonometry is needed to find unknown sides and angles of triangles.
