First subtract from both sides: Divide both sides by 10 The right side is negative. The left side is a sine. The sine is negative in QIII and QIV. The 2 particular solutions in [0,2p) are, from the unit circle 4p/3 and 5p/3. , , , , , The exact general solutions are found by adding 2p∙n to the exact particular solutions in [0,2p), where n is any integer positive, negative or 0. So the general solutions are: If you like you can do a little work on those exact general solutions and get Edwin