Question

How do you evaluate `4 cos^2(-pi/2)`?

Answer 1

As `cos(-\pi/2)=0`, `4cos^2(-pi/2)=4(0^2)=0`.

Explanation:

Remember that any multiple of `\pi` plus or minus `\pi/2` gives a cosine equal to zero.

Just a multiple of `\pi` gives a sine equal to zero.