3.
Solve the Poisson equation with boundary conditions:
$\frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} = -64xy, \quad 0 \leq x \leq 1, \; 0 \leq y \leq 1$
$u(0,y) = 0, \; u(x,0) = 0, \; u(1,y) = 150, \; u(x,1) = 150, \; h = \frac{1}{3}$
[5]