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

The Cosine Rule – Find a Side (1/2) b B c2 = a2 + b2 – 2ab Cos C a C b2 = a2 + c2 – 2ac Cos B a2 = b2 + c2 – 2bc Cos A To use the Cosine Rule – Area we need … two sides and … the angle between them. Web

The Cosine Rule – Find a Side (2/2) c2 = a2 + b2 – 2ab Cos C c 6 30o 7 c2 = 62 + 72 – 2 x 6 x 7 x Cos 30 c = 62 + 72 – 2 x 6 x 7 x Cos 30 = 3.500552254 ≈ 3.5 Web 3