1. The problem statement, all variables and given/known data Prove that the magnitude of the impact parameter B equals the length (-b) of the hyperbolic semiminor axis. 2. Relevant equations |B|=|b|=|a|sqrt(e^2-1) 3. The attempt at a solution I really don't know where to start. I was thinking of finding a relation between a and b but that is just the right hand side of the equation above (for hyperbolic geometry). I was thinking about the Pythagorean theorem, but then I don't know how |B|=|a+b| would become |a|sqrt(e^2-1). Could anyone help me along the right direction? Thanks.