1. The problem statement, all variables and given/known data Simplify this expression. sin(2* arcsin(x/3)) 2. Relevant equations 3. The attempt at a solution Let t = arcsin(x/3), we get sin(2t) which is double angle sin(2T) = 2 sinT cosT I did cosT first T = arcsin x/3, and we know inverse of arcsin is sin T = x/3 this gives us the hypotenuse 3, and opposite side = x (3sin delta = x) using the identity of cos^2 + sin^2 = 1, and solve for cos, I get cosT = sqrt(9-x^2) This is corrected. Now, solve for sinT. sin(arcsin(x/3)), is the same as just x/3, by definition I think. Well, the answer the book gave was 2x/9 * cosT I get the cosT part right, but now the x/9 I don't understand how he produced the number 9. Thank you. I have an exam so please pardon me posting so many questions these two days.