u(r, θ) satisfies Laplace's equation inside a 90º sector of a circular annulus with
a < r < b ; 0 < θ < π/2 . Use separation of variables to find the solution that
satisfies the boundary conditions
u(r, 0) = 0 u(r, π/2) = f(r) ; a < r < b
u(a, θ) = 0 u(b, θ) = 0 ; 0 < θ < π/2
Consider all...