Hi everyone, I'm sorry to bother you with such a trivial question but I really am stuck here. I don't know why I can't prove this one as I've managed to get harder ones than this, but as it is I need help with it. This is the question: Prove 1-cos2x+sin2x = tanx 1+cos2x+sin2x I saw that there was there cos2x and sin 2x and substituted the double angle identities for them, but one I had substituted them and simplified them I was hopelessly stuck on them, no matter what I tried to do I couldn't get any farther with them. I've been doing nothing but math for two days now so I must have fried my brain or something. Any help you guys can give me I would really appreciate, I honestly don't know what I'm doing wrong. I'm sure it's going to end up being something terrible stupid but I thought I had better just ask. Oh and I have one more quick question! If you have a question like: (sin^4)x-(cos^4)x = 1 (sin^2)x-(cos^2)x Can you just simplify by dividing the equation and getting (sin^2)x + (cos^2)x. And then that identity is one of the Pythagorean identities that end up equalling one, so that is the proof? Again sorry for the stupid question, I appreciate all the help anyone can give me on this.