What have you tried so far?
Have you written (1,2) as a linear combination of the eigenvectors?
If so, remember that if x1 and x2 are the eigenvectors, with eigenvalues lam1 and lam2, then Axi = lami xi, so also A(a x1 + b x2) = a lam1 x1 + b lam2 x2. Then you can find A^n (a x1 + b x2) by repeatedly multiplying by A.
Let us know if you're still stuck.