1. The problem statement, all variables and given/known data Let P be any point (except the origin) on the curve r=f(θ). If ψ is the angle between the tangent line at P and the radial line OP, show that tan(ψ)= (r/(dr/dθ)) Hint: Observe that ψ = φ - θ in the figure. 2. Relevant equations Very few equations come to mind except y = r*sin(θ) and x = r*cos(θ). Also, dr/dθ is equal to f'(θ). 3. The attempt at a solution See Relevant Equations.