2) In S_5, how many elements x are there such that x^5=identity?
3) Let H be a subgroup of a group G. Find a bijection between the set of left cosets with respect to H and the set of right cosets with respect to H.
4) Let H be a subgroup of a group G. If [G:H]=2, prove that H is a normal subgroup of G.
5) Let f be an homomorphism from the group of integers Z to itself. Show that f is completely determined by its action on 1: If f(1) = r, then f is multiplication by r; in other words, f(n) = rn for every integer n.