I have the examples above and we are supposed to get the volume of each based on the cross sections above. The circle is x^2+y^2=16

Given that Volume = integral between a and b of A(x) dx so I came up with:

Circle: 4 (integral between -4 and 4) (16-x^2) dx

Eq Tri: (integral between -4 and 4) (sq rt 3) (16-x^2)

Semi: (integral between -4 and 4) (pi/2) (16-x^2)

Isoc: (integral between -4 and 4) (16-x^2)

But those aren't working out?