Show that Eq. (8.2) is a solution of Eq. (8.1) by the following method. Assume the point

Question:

Show that Eq. (8.2) is a solution of Eq. (8.1) by the following method. Assume the point particle to be at the origin, r = 0, and to produce a spherically symmetric field. Then use Gauss' law on a sphere of radius r to conclude
dϕ/dr = Gm/r2.
Deduce Eq. (8.2) from this. (Consider the behavior at infinity.)