Volume enclosed by a sphere
= Volume enclosed by a sphere
{title2=$V=4\pi a^3/3$}
The solid ball inside a radius-$a$ <sphere> has <volume> $4\pi a^3/3$. One derivation integrates concentric shell area: $V=\int_0^a4\pi r^2dr$. The sphere itself is the boundary surface; its area is $4\pi a^2$, a different dimensional quantity.