Solve the following boundary value problems by first obtaining the general solutions of the partial differential equations:
(a) ∂²u/∂x² = 1/c² ∂²u/∂t², given u(x, 0) = 0, (∂u/∂t)t=0 = 1/(1+x²).
(b) ∂²u/∂x² = 2xy, given u(0, y) = y², and (∂u/∂x)x=0 = y.
(c) ∂²u/∂x∂y = 1, given u = 0, ∂u/∂x = 0 on x + y = 0.