Given any triangle abc with corresponding side lengths a, b, and c, the law of cosin states

The Law of cosines equation varies depending on the information that is given.

a² = b² + c² - (2) (b) (c) cos A

b² = a² + c² - (2) (a) (c) cosB

c² = b² + a² - (2) (b) (a) cosC

The lower case letters are the side lengths while the capital letters are the angle measures.