Paper 4, Section II, H
Part II, 2014
(i) Let be a finite subgroup of the multiplicative group of a field. Show that is cyclic.
(ii) Let be the th cyclotomic polynomial. Let be a prime not dividing , and let be a splitting field for over . Show that has elements, where is the least positive integer such that .
(iii) Find the degrees of the irreducible factors of over , and the number of factors of each degree.