Answer
$a.\quad $Solid shell enclosed by the concentric spheres of radii 1 and 2, centered at the origin (the spheres are included).
$b.\quad $The upper half of the solid ball of radius 1, centered at the origin.
Work Step by Step
$x^{2}+y^{2}+z^{2}=1$
is a sphere of radius 1, centered at the origin.
$x^{2}+y^{2}+z^{2}=4$
is a sphere of radius $2$, centered at the origin.
$a.\quad $
These are points between the concentric spheres of radii 1 and 2, centered at the origin (the spheres are included).
$b.\quad $
This describes points within the sphere of radius 1, centered at the origin, above or on the xy-plane.
This describes the upper half of the solid ball of radius 1, centered at the origin.
