if g(x) = cos 2x, find g(pi/2), g(pi/4), g(-x), g(pi - x), g(pi+x), g(x-pi/2)

all you have to do is plug in the value for x

 

cos2(pi/2) = cos pi which = -1

cos2(pi/4) = cos pi/2 which equals 0

and so on