1. The problem statement, all variables and given/known data Find the length of the path traced out by a particle moving on a curve according to the given equation during the time interval specified in each case. The equation is r(t) = a(cos t + t sin t)i + a(sin t - t Cos t)j, 0</=t</=2pi, a>0 2. Relevant equations Arc length = interval (r'(t)dt) 3. The attempt at a solution I found the derviative of r(t) to be r'(t) = cost + tsint +atcost +sintt -tcost +atsint Integrating this from 0->2pi I keep getting 0 because it is subtracting itself. The answer is supposed to be 2pi2a. What am I doing wrong?