Worked like a charm! Thanks very much.
I knew to represent ##r## that way, but I didn't think to bring in the new index ##l## when I did the chain rule. So I had these new mis-indexed ##x^k## terms that messed me up.
In retrospect, I can sort of see why we're summing over the index ##l##...
I'm working through A. Zee's new EGR book, and I came to a step on tidal forces I couldn't follow. He presents the gravitational potential
V(\vec{x})=-GM/r
and asks us to verify that the tensor R^{ij}(\vec{x})\equiv\partial^{i}\partial^{j}V(\vec{x}) is, in this case...