I have an exercise: Find the normal curvature of the Viviani curve on the sphere $$r = R[\text{sin}ue(v)+\text{cos}(uk)]$$ at any point and at points along the z axis
legend: $$r=\phi(v)e(u) + \psi(v)k$$ $$z=\psi(v), y=\phi(v)$$
This problem is from a book on differential geometry. I don't know how to solve it and have no one to ask.