4. An iterated integral over a rectangle [(1, b] x [c, d] where the integrand can be factored as f (z, y) = g(z)h(y) b a b d can itself be factored as f f f (3.31) dy aim = (/ 9(3) 031:) (f My) 013;). Verify this by evaluating a c a c 2 3 f f Iyz dy dc: twice: as an iterated integral, and as the product of two integrals. o o