The Cosine Rule

The Cosine Rule

1. To find a missing side

   • a = b + c - 2bc cos A

2. To find the missing angle

   • cos A = b + c - a 2bc

3. The cosine rule applies to any triangle, you don't need a right angle.

4. You usually use the cosine rule when you are given two sides and the included angle (SAS) or when you are given three sides and want to work out an angle (SSS)