verify the identity.

Question

cos(nπ+θ) = (-1)^n cos θ  , n is an integer

Answer 1

Step 1:

The identity is

Consider the left hand part 

Recall the trigonometric identity

                    (Since )

For even multiples of cosine function value is 1 and for odd multiples of cosine function value is -1.

Solution:

The identity is verified.