For each of the following integrals,
(i) evaluate the given integrals,
(ii) interchange the order of integration and evaluate.
(a) 1J0 1Jx xy^3 dy dx
(b) 1J0 √xJx^2 √x-y dy dx

7. Evaluate the following double integrals by changing the order of integration.
(a) 1J0 1Jx sin(y²) dy dx
(b) 3J0 9Jy^2 y cos(x^2) dxdy