The problem:

y'' + 9y = 9sec^2(3t) 0 < t < pi/6

So I make it homogenous by setting y''+ 9y = 0

getting 3i repeating.... y = C1cos(3t)+C2sin(3t)

From there.. I'm not sure what to do with the 9sec^2(3t). Please help, I have a quiz later today, thanks!