(4) An ant is moving on the surface z = x+y+ y such that its x- and y-coordinates satisfy Sx x = cost, y = sint. Use chain rule to find Note: writing z as a function of t will not earn you credits. You may use it to check your answer, though. (b) Find the values of t in [0,2] for which the ant is moving uphill. Hint: the identity cos(2t) = cos t- sin?t might be useful.