1. The problem statement, all variables and given/known data The motion of a particle is described by x = 10 sin (piet +pie/2 ). At what time ( in second ) is the potential energy equal to the kinetic energy ? 2. Relevant equations KE = 1/2 mv^2 PE=1/2 Kx^2 3. The attempt at a solution V=pie10cos(piet + pie/3) V^2 = pie^2 100cos^2(piet+ pie/3) KE = mpie5ocos^2 (piet + pie/3) X^2 =100sin^2(piet +pie/2 ) PE =k50 sin^2(piet +pie/2 ) KE=PE pie^2 100cos^2(piet+ pie/3) =K50 sin^2(piet +pie/2 ) m/k * pie^2 = tan^2(piet +pie/2 ) take square root of both sides of equation 1/pie * pie = tan(piet + pie/3) piet + pie/3 =tan-1(1) solving for t i get a negative value where iam i going wrong.