|a|=p,
则a^-1^p=a^p^-1=e^-1=e因此|a^-1|=|a|
且（(x^-1)*a*x）^p=(x^-1)*a*x (x^-1)*a*x.(x^-1)*a*x,即p个(x^-1)*a*x
=(x^-1)*a*（x(x^-1)）*a*（x(x^-1)）*a*x.=(x^-1)*a^p*x=(x^-1)*x=e后一个证毕