How to solve the equation?

Sat, 2008-01-19 00:44 - V.Gnanaraj

I have come accross an equation of the form ∂2u/∂x2 + ∂2u/∂y2 - K2 u =0 with the following conditions. y ≥αx,y ≥-αx, x=H.How to solve this equation?.analytically.