Right, but I don't think his intent was to show who killed JFK; just how it could be done. I.e., JFK's backward's head reaction can be caused solely by a shot from behind. If we include this with the other evidence - the Z-film, the autopsy, the x-rays - then reasonable people can agree that a shot from behind killed JFK. No GK shot was necessary to explain JFK's reaction.
As to the math: Yeah, anything above, if I can remember any of it, calculus is beyond my pay scale. What's remarkable is that this is the type of stuff that Luis Alvarez did on the back of an envelope on a plane ride home. Easy peasy. Alvarez worked on the Manhattan Project - he designed from scratch the implosion mechanism/devices used on Fat Man; he was on the plane monitoring the Hiroshima bombing; he won the Nobel Prize for his work on developing the hydrogen bubble that was used to study particle physics; and he discovered the remains of the asteroid that likely wiped out the dinosaurs. Among other things <g>.