6. In an inverse square force field, where c is a constant and , find the work done in moving a particle along the line from (1, 1, 1) to (3, 3, 3). (15%)
5. Evaluate sin(x+2y) cos(x-2y) dA over the region R = {(x, y) | x ≥ 0, y ≥ 0, x + 2y ≤ 2π}. (15%)
4. Find the point on the intersection of the plane and the paraboloid that is closest to the origin. (15%)