In the Jan 2013 paper Q3bii there are 3 values for x given in the mark scheme of 90°, 45°, 135°. I've solved cos2x = 0 in the range 0° < x < 180° and come out with 45° and 135°. Can someone point out what I've forgotten :/?
I'm pretty sure cos(2x90) =/= 0...