1. The problem statement, all variables and given/known data Use a parametrization to find the flux across the surface in the given direction: F = (2xy)i + (2yz)j + (2xz)k upward across the portion of the plane x + y + z = 2a that lies above the square 0 <= x <= a, 0 <= y <= a, in the xy-plane. 2. Relevant equations Flux = Double integral of F dot n d(sigma), where d(sigma) = |(r_u x r_v)| du dv x = cross product 3. The attempt at a solution I need some help coming up with a parametrization for the plane x + y + z = 2a. Since it lies in the xy-plane, I figured I can use the parametrization x = u and y = v, so I get u = 2a - v, and v = 2a - u, and z = 2a - u - v, and use order of integration du dv. However, I end up with a rather large integral with this parametrization, so I just want to make sure I'm doing this right before trying to solve it. Thanks for any suggestions!