Trigonometry gets confusing at angles bigger than a right angle because you can’t draw a little triangle and say ‘opposite over hypotenuse’ or whatever.
Rather than adopt some kind of handle-turning approach (eg C.A.S.T.), that may get you the correct result but which doesn’t add to understanding, try thinking in terms of the graphs of the trig. functions eg Sin x. This allows you to use the symmetry in these plots to see why you get the answers (rather than just remembering some opaque formula).
