Definition 17: Let H is a subgroup of the group G. The number of all right cosets(left cofets) of H is called index of H n g E;+ is a subgroup of z;+ K Es index?? Theorem 6.20: Let g be a finite group and let h be a subgroup of G. Then G is a multiple of H Example: Let g be a finite group and let the order of a in G be n Then n G. Definition 17：Let H is a subgroup of the group G. The number of all right cosets(left cofets) of H is called index of H in G.  [E;+] is a subgroup of [Z;+].  E’s index?？  Theorem 6.20: Let G be a finite group and let H be a subgroup of G. Then |G| is a multiple of |H|.  Example: Let G be a finite group and let the order of a in G be n. Then n| |G|