Hi everybody, this problem is giving me trouble and I was wondering if you could give me any advice. 1. The problem statement, all variables and given/known data The velocity of an object in simple harmonic motion is given by vx(t)= - (0.35 m/s)sin(20t + pi), where t is in s. What is the first time after t=0s at which the velocity is - 0.25 m/s? 2. Relevant equations See the equation above. 3. The attempt at a solution I simply plugged -.25 m/s in for vx(t) above and solved for t, so I got: -0.25 = -0.35sin(20t + pi) .714 = sin(20t + pi) When I solve for t I get t = -.397e-1 = -.0397s, but mastering physics (the program I use to do homework online) say it's wrong. I entered the answer as positive. Anybody have any idea? Thanks a lot! edit: I just went to see my professor and he helped me set it up, when finished we had sin(20t) = -5/7, but master physics says it's wrong.