Senior high school mathematics needs four trigonometric functions to solve this problem. Thank you for the process.
Because the image of the function y=f(x) is symmetric about x=π/4.
therefore
( 1)f(-π/2)=f(π)=0，f(-π/4)=f(3π/4)=√2/2
(2) When -π/2
Because π/4 =
So when -π/2
When π/4 =