#x = t sec( t/3 - pi ) = t sec ( pi - t ) = - t sec t#
#(dx)/(dt) = - sec t - t sec t tan t = - sec t ( 1 + t tan t )#
#y = t cos ( pi - t ) = - t cos t#
#(dy)/(dt) = - cos t + t sin t#
#(dy)/(dx) = (dy)/(dt)/(dx)/(dt)#
#= ( cos t - t sin t )/( sec t ( 1 + t tan t ))#
#= (cos^2t ( cos t - t sin t ))/( cos t + t sin t )#