[2] Multivariable Integral Part
(1) Evaluate the following integral by first reversing the order of integration:
∫∫(y^3+1)dydx
(2) Derivation process is necessary. Find the Jacobian for the transformation x=r cos(y) and y=r sin(y).
(3) Find ∫∫dxdy, where R is the area surrounded by curves xy=1, xy=2, xy=1, and xy=3.