Question

How do you express `cos( (3 pi)/ 2 ) * cos (( 3 pi) /8 )` without using products of trigonometric functions?

Answer 1

`cos({3pi}/2) * cos({3pi}/8) = 0`

Explanation:

`cos(x) = 0` when `x = pi/2, {3pi}/2, {5pi}/2 ...`

This is a graph of `y=cos(x)`
graph{cos(x) [-10, 10, -5, 5]}
`cos({3pi}/2) = 0`

`cos({3pi}/2) * cos({3pi}/8) = 0 * cos({3pi}/8)`

`= 0`