Question

How do you express `cos(pi/ 2 ) * cos (( 11 pi) / 12 )` without using products of trigonometric functions?

Answer 1

`cos(pi/2)*cos(11pi/12)=0`

Explanation:

As `cos(pi/2)=0`, its product with any number will be `0`. Incidentally `cos(11pi/12)` is non-zero.