if a sphere is of the equation $r^2 = x^2 + y ^2 +z ^2$ and we want to find a hemisphere does that just involve setting a limit to be half of the radius ?

For example if we know that the centre of the sphere sits at $(2,1,0)$ and the radius is $2$, then if we set the limit of z to be from 0 to 1 then that would be the top half of the sphere ?

$2^2 = (x-2)^2 + (y-1)^2 + (z)^2$ and the limit would be from $z = 0$ to $z = 1$.

Is that right ?