7. The general solution of the equation y" - 6y' + 9y = 0 is (a) ciesz + Cze-3x (b) e3x (1 + C2) (c) x3(c1 + (2 In |x]) (d) cle3 + cze3x In lac| 8. The solution of the initial-value problem y" +16y = 0, y(0) = 0, y'(0) = 12 is y = (a) 3 sin(4x) (b) (ex - e-4x) (c) 12 sin(4x) (d) 12 cos(4x) 9. The general solution of the equation x2y" - 4xy' + 6y = 0 is y = (a) 142 + C2x3 (b) Cle2 + cze3x (c) e2x [c1 cos( V2x) + C2 sin(V2x) ] (d) x2 [c1 cos( v2 In (x]) + c2 sin( v2 In (x)] 10. The general solution of the equation y" - 4y = 24el is y = (a) 2etz + 1 cos(2x) + C2 sin(2x) (b) 24 + Cle2 + Cye-2x (c) 2xe4x + Cle2x + Cze -2x (d) 2.2e4 + Cle27 + Cze -2x