1. The problem statement, all variables and given/known data Uxx +u(x,y)=0 2. Relevant equations ? 3. The attempt at a solution Step 1) u(x,y)=A(x)B(y) Step 2) uxx=d^u/dx^2 Step 3) d^u/dx^2 + A(x)B(y) = 0 Step 4) d^u/dx^2 = -[A(x)B(y)] (?) I have no idea what I'm doing, so small words would be useful.