Consider the PDE u_x + 4u_y = 0.
(a) Find the most general solution to this PDE.
(b) Solve the PDE, subject to the extra condition u(x_0, 0) = 2x_0 + sin x_0.
(c) Can we prescribe initial data u(x_0, x_0^2) = x_0? Justify.
(d) Find the most general solution to the PDE u_x + 4u_y = x^2 + cos y.