trig
posted by anna .
inverse cos (rad2/2)=135 degrees
inverse sin (rad2/2)=45 degrees
I don't understand why cos is 135

for the cosine = sqrt 2/2 negative x axis
means quadrant 2 or quadrant 3
It could be either 180 + 45 or 180  45
so either 135 or 225
for the sine = sqrt 2/2
means quadrant 3 or quadrant 4
that is 180 + 45 or 360  45
so either 225 or 315
225 satisfies both the sine and the cosine.