Well, what did you get for the homogeneous solution?
Which method(s) include in your course to find yp ?
undetermined coefficients deals only with exponentials, sines, cosines , polynomials or products of those.
you can not use UC when the right hand side contains tangent term.
Try Variation of Paramters or Reduction of Order Methods.
Let see your start for this problem?
We do not give full solutions here.
Inverse Differential Operators can not be used for the tangent
Sorry I remove it from my 1st reply
Actually IDO can be applied for same types of function which can be solved by UC
Only variation of parameters and reduction of order can be used here.
(Theoretically you can do a series solution, but it will be crazy!)