1. The problem statement, all variables and given/known data Riccati sets y/x=q and then arrives at x^2*dq. This is his analysis of Jacob Hermann's differential equations criticised by Johannes Bernoulli (published in 1710). x*dy-y*dx is a constant and is equivalent to dt. I have understood everything except for the q-substitution. 3. The attempt at a solution Well, I have tried several times but all my solutions are not correct. E.g. x*dx*(dq-q). I have no idea how he got this square. I am missing some clues.