Solve using variation of parameters y" + 9y = 3 sec(3t) O ci cos(3t) + c2 sin(3t) + - sin(3t) - 3 In sec(3t) | cos(3t) O ci cos(3t) + c2 sin(3t) + = sin(3t) - -In sec(3t) | cos(3t) O ci cos(3t) + c2 sin(3t) + t sin(3t) - 2In sec(3t) | cos(3t) O ci cos(3t) + ca sin(3t) + 4 sin(3t) + 2 In sec(3t) | cos(3t) O ci cos(3t) + c2 sin(3t) + t cos(3t) - 3 In sec(3t) | sin(3t)