Is the root of the characteristic equation 0 I,

Let J = 1, and the special solution form is y = x (acosx+b sinx);

If we change the topic, the left end is the same, and the non-homogeneous term at the right end is (1/2)cos2x, that is, α iβ = 0 2i.

Is not the root of the characteristic equation 0 I,

Let J = 0, and the special solution form is y = Acos2x+Bsin2x.