Question

State the law of cosines.

Answer 1

As per the cosines law formula, to find the length of sides of triangle say △ABC, we can write as;

• a^2 = b^2 + c^2 – 2bc cos α

• b^2 = a^2 + c^2 – 2ac cos β

• c2 = b2 + a2 – 2ba cos γ

And if we want to find the angles of △ABC, then the cosine rule is applied as;

• cos α = [b^2 + c^2 – a^2]/2bc

• cos β = [a^2 + c^2 – b^2]/2ac

• cos γ = [b^2 + a^2 – c^2]/2ab

Where a, b and c are the lengths of sides of a triangle.