I need help with these questions

21. Two spacecraft are following paths in space given by r; = (sin I, t, :2) and r2 = (003131 t, :3). If the temperature for points in space is given by T(x, y,z) = x2y(1 2), use the Chain Rule to determine the rate of change of the difference D in the temperatures the two spacecraft experi- ence at time t = 31'. - 23. Let u = u(x, y), and let (r, 0) be polar coordinates. Verify the relation 1/ Vull 2 = u ? + 8 Hint: Compute the right-hand side by expressing ue and up in terms of ux and uy. 24. Let u(r, 0) = r2 cos2 0. Use Eq. (8) to compute || Vu ||2. Then compute II Vul/2 directly by observing that u(x, y) = x2, and compare