use this u wll get right answer pg 523 of rosen 7th edition
Suppose that {an} satisfies the linear nonhomogeneous recurrence relation an = c1an−1 + c2an−2 +···+ ckan−k + F (n), where c1, c2,...,ck are real numbers, and F (n) = (btnt + bt−1nt−1 +···+ b1n + b0)sn, where b0, b1,...,bt and s are real numbers. When sis not a root of the characteristic equation of the associated linear homogeneous recurrence relation, there is a particular solution of the form (ptnt + pt−1nt−1 +···+ p1n + p0)sn. When s is a root of this characteristic equation and its multiplicity is m, there is a particular solution of the form nm(ptnt + pt−1nt−1 +···+ p1n + p0)sn.