a) x = C1 et + C2e-t - t - 1, y = C1et - C2e-t - t - 1; °b) y = ex(C1 sin x + C2 cos x) - 15 sin x - 25 cos x, z = ex (-C1 cos x + C2 sin x) + 2
5 sin x - 1
5 cos x; °c) y = C1x + C2/x2 + 1
3x ln |x|, z = (2
3 - C1)x2 + 2C2/x - 1
3x2 ln |x|.