The Law of Cosines

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

c² = a² + b² − 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;

a² = b² + c² − 2bc cos(A)

b² = a² + c² − 2ac cos(B)

c² = a² + b² − 2ab cos(C)

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