Hi, I had to solve without the aid of a calculator: 2cos(x) = sin(2x) What I did was perform the following substitution: 2cos(x) = 2sin(x)cos(x) I then cancelled and got: sin (x) = 1 For 0 to 3pi, I got two answers, pi/2 and 5pi/2. I did not get one of the answers. Why? What did I do wrong? Thanks!