Prove the Poisson Integral Formula, that is, prove that if u ā C^2(Ä(0, R)) with Ä(0, R) ā ā^N, and -āu = 0 in Ģ, then u(Ī) = (R^2 - |Ī|^2) / (Ģ_N R) ā«_{āB(0,R)} u(x) / |x - Ī|^N dĢ(x), with Ģ_N being the measure of the boundary (of dimension N - 1) of the unit ball.