- Use the change of variables to evaluate [(x + y) + 2] (x y)dA around the region R{(x, y): x 0, y 0, x + y = 1} by using the new variables: u = x - y, v = x + y - Use the change of variables to evaluate f(x+y)(x-2y)dA around by using the new the region R{(x, y): x 0, y 0, x + y = 1} variables: u = x - 2y, v = x + y - Use the polar coordinates to find the volume inside the paraboloid z = x + y for 0 z 1 - Use the polar coordinates to find the volume inside the cone z = for 0 z 1/ x + y