The Law of Cosines is useful when solving for SAS or SSS triangles.
$$ a^2 = b^2 + c^2 -2bc\cos(\alpha) $$
$$ b^2 = a^2 + c^2 -2ac\cos(\beta) $$
$$ c^2 = a^2 + b^2 -2ab\cos(\gamma) $$ 
- When using the Law of Cosines to solve for SSS triangles, start solving for the largest angle.
- When correctly solved, the smallest angle will be opposite the smallest side, and the largest angle will be opposite the largest side.