Question

How do I find the value of cos 9π/4?

Answer 1

`cos((9pi)/4) = sqrt(2)/2`

Explanation:

`(9pi)/4 = 2pi +pi/4`

So cos((9pi)/4) = cos(pi/4)#

`pi/4` is one of the standard triangle angles
and `cos(pi/4) = sqrt(2)/2 (or 1/sqrt(2))`