Question: 1. A change of coordinates x = x(s, t), y = y(s, t) where the rectangle 0 ≤ s ≤ 1, 0 ≤ t ≤ 1 in the st-plane corresponds to a different rectangle in the xy-plane.
2. A change of coordinates x = x(s, t), y = y(s, t) where every region in the st-plane corresponds to a region in the xy-plane with twice the area.