## College Algebra 7th Edition

$V(r)=4\pi r^3$, $r>0$
We know that the volume of a cylinder is: $V=\pi r^2h$ We are told that the height is four times the radius ($h=4r$). So: $V=\pi r^2h=\pi r^2*4r=4\pi r^3$ (with $r>0$).