Question

Please help! Desperate! need help with both but will take help on just one! see attached

Answer 1

Question 4:
Changing to polar coordinates gives
\[\int\limits_{0}^{\pi}\int\limits_{0}^{a}(a ^{2}-r ^{2})r dr d \theta\]This can be worked out easily
\[\pi \left[ a ^{2}r ^{2}/2 - r ^{4}/4 \right]_{0}^{a} = \pi a ^{4}/4\]

Answer 2

THANKS