In any given triangle a, b, and c are the sides of the triangle and also opposite angles are A, B, and C.

Then the Cosine Rule states

**c ^{2} = a^{2} + b^{2} − 2ab cos(C)**

It is also called **The Law of Cosines**

## Formulas (Versions for a, b and c)

According to the cosines law formula, to check the length of sides of triangle say △ABC, we can see below as;

**a ^{2} = b^{2} + c^{2} − 2bc cos(A)**

**b ^{2} = a^{2} + c^{2} − 2ac cos(B)**

**c ^{2} = a^{2} + b^{2} − 2ab cos(C)**

## Find the angles of triangle

And if we want to calculate the angles of triangle, then the cosine rule is followed as;