Use variation of parameter method to solve the differential equation y"+y=secx.
Okay, I did! Turned out to be very easy. But wouldn't it be better for YOU to solve the equation yourself? Or at least try.
Do you know what the "variation of parameters method" is?
Do you know how to find the general solution to the associated homogeneous equation?
And as has been stated twice above, you should show us what you did and what your answer is, so we can CHECK it, rather than us giving you the solution and answer on the off chance that you actually did do some of the work yourself.