What is the Cosine Rule?
- The cosine rule can be used to find the length of one side if two sides and their combining angle are known.
- Alternatively, the cosine rule can be used to find an angle if all 3 sides of a triangle are known.
- The cosine rule is applicable to all triangles, not just right ones!
Proof
Sources
https://www.teachoo.com/7253/2244/Law-of-Cosine-(Cosine-Law)/category/Sine-and-Cosine-Formula/