ABSTRACT
With reference to triangle ABC of Figure 23.1, the cosine rule states
a2 = b2 + c2 − 2bc cos A or b2 = a2 + c2 − 2ac cos B or c2 = a2 + b2 − 2ab cosC The rule may be used only when
(a) 2 sides and the included angle are initially given, or
(b) 3 sides are initially given.
