Calculus [Finding volume of solid]
posted by Ali .
Find the volume of the solid obtained by rotating the region bounded by the given curves about the specified axis.
y=x^2
y=0
x=3
about the yaxis

make a sketch
this one is easier than the others you posted
volume about the yaxis
= π∫x^2 dy
= π∫y dy from y = 0 to 9
= π [ (1/2)y^2 ] from 0 to 9
= π (81/2  0)
= 81π/2