$\displaystyle y'' +4y=6xcos(2x)$

I am using the method of undetermined coefficients. I had no trouble solving for the homogeneous solution, but the particular solution has me baffled. I used $\displaystyle y_p=Axcos(2x)+Bxsin(2x)$. After finding the derivatives of this and putting them back into the original equation, I end up with a system of equations that I cannot solve. Have I chosen this function poorly?