We can set up a coordinate system in which the sphere has center at the origin and the given point, m, is on the z-axis. The equation of the sphere in that coordinate system is and m is (0, 0, l). Given a point (x, y, z) on the sphere, above the xy-plane, then then the distance from m to that point is . If (x, y, z) is below the xy-plane, then the distance is .