Note: In any ΔABC we define ‘a’ as length of side opposite to ∠A , ‘b’ as length of side opposite to ∠B and ‘c’ as length of side opposite to ∠C .

Key point to solve the problem:

Idea of cosine formula in ΔABC

•

Cos A =

• Cos B =

• Cos C =

As we have a = 18, b = 24 and c = 30

∴ Cos A =

Cos B =

Cos C =