(c) Prove that for every divisor d of n, Zn has a unique subgroup of order d. (Hint: What is the order of the element "?)

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter4: More On Groups
Section4.4: Cosets Of A Subgroup
Problem 32E: (See Exercise 31.) Suppose G is a group that is transitive on 1,2,...,n, and let ki be the subgroup...
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3. We showed in class that every subgroup of a cyclic group is cyclic. Let n e N.
(a) An integer combination of two numbers m and n is a number of the form mx+ny, where
x, y E Z. A result in number theory (see Pinter p. 219) says that a number a is an integer
combination of m and n if and only if a is a multiple of gcd(m, n) (and as a consequence,
gcd(m, n) is the smallest positive integer combination of m and n). Use this to prove
that if m e Zn, then (m) = (gcd(m, n)). (Hint: xm = xm + ny (mod n).)
(b) Use this to fill in details of the result in class that if m e Zn, then ord(m)
gcd(m,n)*
(c) Prove that for every divisor d of n, Zn has a unique subgroup of order d. (Hint: What is
the order of the element ?)
Transcribed Image Text:3. We showed in class that every subgroup of a cyclic group is cyclic. Let n e N. (a) An integer combination of two numbers m and n is a number of the form mx+ny, where x, y E Z. A result in number theory (see Pinter p. 219) says that a number a is an integer combination of m and n if and only if a is a multiple of gcd(m, n) (and as a consequence, gcd(m, n) is the smallest positive integer combination of m and n). Use this to prove that if m e Zn, then (m) = (gcd(m, n)). (Hint: xm = xm + ny (mod n).) (b) Use this to fill in details of the result in class that if m e Zn, then ord(m) gcd(m,n)* (c) Prove that for every divisor d of n, Zn has a unique subgroup of order d. (Hint: What is the order of the element ?)
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