Differentiation Help!! 1. The problem statement, all variables and given/known data A particle is moving along a straight line so that, at time t seconds after leaving a fixed point O, its velocity vms-1 is given by v=10sin(1/2 t). Find the time when the acceleration, given by dv/dt, is first zero. 2. Relevant equations sinx differentiates to cosx 3. The attempt at a solution Ok i know they are asking me to find the time where there is a stationary point so therefore the gradient or dv/dt = 0. From differentiating 10sin(1/2 t) i got 5cos(1/2 t). so therefore, 5cos(1/2 t)=0 so i thought you multiply by 2 to get rid of the half then divide by 10 so the Right hand side= 0 and then inverse cos of 0 = 1/2 Pi but the answer in the textbook gives Pi. Please help me any body!!