pls give me some hint

(7) Let I be a line through 0 in R and a > 0 be any angle. Let Fi be the reflection nin I and Ra be the rotation by a around 0. Let H = (Ra, Fi) C O(2) be the subgroup of O(2) generated by Ra and Fi. Prove that H = {FFR. | k = 0, 1; n EZ}. Hint: Show that Fio Ra = R_a . Fi