Use superposition to solve the following inhomogeneous ordinary differential equations:
(a) u' + 2u = 1 + cos x
(b) u" - 9u = x + sin x
(c) 9u" - 18u' + 10u = 1 + ex cos x
(d) u" + u' - 2u = sinh x, where
Sinh x = 1/2 (ex - e-x)
(e) u"' + 9u' = 1 + e3x