Thank you @haruspex and @Orodruin! I have solved the problem now.haruspex said:Your working headed off into a blind alley. You know that you need to be eliminating A, so tucking it inside an arccos function isn’t going to get you there.
Start by writing all three initial state equations: position, velocity and acceleration. Then see how you can combine them to eliminate one of the unknowns.
Thanks @haruspex! I did understand your comment, which I agree, would be very useful skill to have!haruspex said:You are welcome. But did you understand my comment about heading off into a blind alley? Recognising which directions cannot lead anywhere is a useful skill to develop.