Chapter 12 - Section 12.1 - Three-Dimensional Coordinate Systems - 12.1 Exercises - Page 797: 41

$r^2 < x^2+y^2+z^2 < R^2$

"between (but not on)...": "spheres of radius r and R centered at the origin": $x^2+y^2+z^2 [< or >] r^2$ $x^2+y^2+z^2 [< or >] R^2$ "r < R": $r^2 < x^2+y^2+z^2 $ $x^2+y^2+z^2 < R^2$ Combine these statements to get: $r^2 < x^2+y^2+z^2 < R^2$