(a) A torus of revolution (doughnut) is obtained by rotating a circle C in the xz-plane about the z-axis in space. (See the accompanying figure.) If C has radius r > 0 and center (1, 0, 0), show that a parametrization of the torus is "(u, v) = [(R + rcos(u)) cos(v)] i + [(R + r cos(u)) sin(v)]j + (rsin(u))k, where 0