1. The problem statement, all variables and given/known data Alright, here's the question, A stream function for a plane, irrotational, polar-coordinate flow is ψ=9r^2sin^θ. Find out the velocity potential in Cartesian Co-ordinate! 2. Relevant equations 3. The attempt at a solution Well, I can easily find out the velocity potential in Polar co-ordinates but then how do I convert it to Cartesian Co-ordinates?