hmm.. if I also use 3\pi/4 then x would = to 3\pi/8 +n\pi, that is on the answer, but \pi/8 +n\pi is not on the answer.
And also, I don't understand how you get 9\pi/8?
Did he just skip the 2st quadrant, and wrote the 2nd answer as going half a circle from the 2nd quadrant instead of using the answer from the 1st?