Does the Triple Integral Formula Apply to a Point-Mass Inside a Spherical Shell?

[cscott]

Does $-Gm\rho2\pi\left(R_2^2-R_1^2\right)$ make sense for the potential of a point-mass "m" inside a spherical shell of radii $R_1< R_2$ and density $\rho$?

Now I've already found the potential outside of a homogeneous sphere of same density. I'm now asked to use these two results to find the potential inside a homogeneous sphere of again indeity density sphere, using the previous two results.

Can I do this by considering the point on the inside of the shell with a sphere in the space in the middle? Does it make sense to add the two potential formulas using the correct radii?

 

[rl.bhat]

Expression for potential is GMm/R. So something is missing in the given expression