Press Ctrl-A ©G Dear2008 – Not to be sold/Free to use Cosine Rule Angles Stage 6 - Year 12 General Mathematic (HSC)

2 The Cosine Rule – Find an Angle (1/2) A a B b C c Cos C = a 2 + b 2 – c 2 2ab Cos B = a 2 + c 2 – b 2 2ac Cos A = b 2 + c 2 – a 2 2bc To use the Cosine Rule – Angle we need … three sides

Cos -1 ( ) 2x7x5 3 The Cosine Rule – Find an Angle (2/2) A 7 B 5 CoCoCoCo 6 Cos C = a 2 + b 2 – c 2 2ab Cos C = – 6 2 Cos C = – 6 2 Cos -1 C = o C ≈ 57 o