The Unit Circle..having a crisis!?

in my book (im studyng for a test) it asks to convert -135 degrees into radians which is easily - 3pi/4. it also asks what quadrant its in. in the back of the book it says its in the third?!! (the book gives answers to odd book probs in the back). it doesnt explain why though. why wouldn't it be in the second? is it because of the negative sign??? what does a neg do to it thoi