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Lagrange theorem states that the order of any subgroup of a group G must divide order of the group G. If order p of the group G is prime the only divisors are 1 and p, therefore the only subgroups of G are {e} and G itself. Take any a not equal e. Then the set of all integer powers of a is by definition a cyclic subgroup of G, but the only subgroup of G with more then 1 element is G itself, therefore G is cyclic. QED.
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Show that an element of a group has order n if and only if it generates a cyclic group of order n?
An element ( g ) of a group ( G ) has order ( n ) if the smallest positive integer ( k ) such that ( g^k = e ) (the identity element) is ( n ). This means the powers of ( g ) generate the set ( { e, g, g^2, \ldots, g^{n-1} } ), which contains ( n ) distinct elements. Therefore, the cyclic group generated by ( g ), denoted ( \langle g \rangle ), has exactly ( n ) elements, thus it is a cyclic group of order ( n ). Conversely, if ( \langle g \rangle ) is a cyclic group of order ( n ), then ( g ) must also have order ( n ) since ( g^n = e ) is the first occurrence of the identity.
How do you prove that order of a group G is finite only if G is finite and vice versa?
(1). G is is finite implies o(G) is finite.Let G be a finite group of order n and let e be the identity element in G. Then the elements of G may be written as e, g1, g2, ... gn-1. We prove that the order of each element is finite, thereby proving that G is finite implies that each element in G has finite order. Let gkbe an element in G which does not have a finite order. Since (gk)r is in G for each value of r = 0, 1, 2, ... then we conclude that we may find p, q positive integers such that (gk)p = (gk)q . Without loss of generality we may assume that p> q. Hence(gk)p-q = e. Thus p - q is the order of gk in G and is finite.(2). o(G) is finite implies G is finite.This follows from the definition of order of a group, that is, the order of a group is the number of members which the underlying set contains. In defining the order we are hence assuming that G is finite. Otherwise we cannot speak about quantity.Hope that this helps.
If PS are distinct primes show that an abelian group of order PS must be cyclic?
If ( G ) is an abelian group of order ( PS ), where ( P ) and ( S ) are distinct primes, then by the Fundamental Theorem of Finite Abelian Groups, ( G ) can be expressed as a direct product of cyclic groups of prime power order. The possible structures for ( G ) are ( \mathbb{Z}/PS\mathbb{Z} ) or ( \mathbb{Z}/P^k\mathbb{Z} \times \mathbb{Z}/S^m\mathbb{Z} ) with ( k ) and ( m ) both ( 1 ). However, since ( P ) and ( S ) are distinct primes, the only way for ( G ) to maintain order ( PS ) while being abelian is for it to be isomorphic to ( \mathbb{Z}/PS\mathbb{Z} ), which is cyclic. Thus, ( G ) must be cyclic.
Can a non-abelian group have a torsion subgroup?
Yes, a non-abelian group can have a torsion subgroup. A torsion subgroup is defined as the set of elements in a group that have finite order. Many non-abelian groups, such as the symmetric group ( S_3 ), contain elements of finite order, thus forming a torsion subgroup. Therefore, the existence of a torsion subgroup is not restricted to abelian groups.
How do you prove that a group of order 3 is cyclic?
Any group must have an identity element e. As it has order 3, it must have two other elements, a and b. Now, clearly, ab = e, for if ab = b, then a = e:abb-1 = bb-1, so ae = e, or a = e.This contradicts the givens, so ab != b. Similarly, ab != a, leaving only possibility: ab = e. Multiplying by a-1, b = a-1. So our group has three elements: e, a, a-1.What is a2? It cannot be a, because that would imply a = e, a contradiction of the givens. Nor can it be e, because then a = a-1, and these were shown to be distinct. One possibility remains: a2 = a-1.That means that a3 = e, and the powers of a are: a0 = e, a, a2 = a-1, a3 = e, a4 = a, etc. Thus, the cyclic group generated by a is given by: = {e, a, a-1}.QED.Let g be any element other than the identity. Consider , the subgroup generated by g. By Lagrange's Theorem, the order of is either 1 or 3. Which is it? contains at least two distinct elements (e and a). Therefore it has 3 elements, and so is the whole group. In other words, g generates the group.QEDIn fact here is the proof that any group of order p where p is a prime number is cyclic. It follow precisely from the proof given for order 3.Let p be any prime number and let the order of a group G be p. We denote this as|G|=p. We know G has more than one element, so let g be an element of the group and g is not the identity element in G. We also know contains more than one element and ||1 such that gn =1 if such an n exists.
Prove that a group of order three is abelian?
By LaGrange's Thm., the order of an element of a group must divide the order of the group. Since 3 is prime, up to isomorphism, the only group of order three is {1,x,x^2} where x^3=1. Note that this is a finite cyclic group. Since all cyclic groups are abelian, because they can be modeled by addition mod an integer, the group of order 3 is abelian.
What is finite and infinite cyclic group?
Normally, a cyclic group is defined as a set of numbers generated by repeated use of an operator on a single element which is called the generator and is denoted by g.If the operation is multiplicative then the elements are g0, g1, g2, ...Such a group may be finite or infinite. If for some integer k, gk = g0 then the cyclic group is finite, of order k. If there is no such k, then it is infinite - and is isomorphic to Z(integers) with the operation being addition.
Prove that the order of an element of a group of finite order is a divisor of the order of the group?
Let ( G ) be a finite group with order ( |G| ), and let ( g \in G ) be an element of finite order ( n ). The order of ( g ), denoted ( |g| ), is the smallest positive integer such that ( g^k = e ) for some integer ( k ), where ( e ) is the identity element. The subgroup generated by ( g ), denoted ( \langle g \rangle ), has order ( |g| = n ). By Lagrange's theorem, the order of any subgroup divides the order of the group, thus ( |g| ) divides ( |G| ).
What is the order of a group?
The order of a group is the same as its cardinality - i.e. the number of elements the set contains. The order of a particular element is the order of the (cyclic) group generated by that element - i.e. the order of the group {...a-4, a-3, a-2, a-1, e, a, a2, a3, a4...}. If these powers do not go on forever, it will have a finite order; otherwise the order will be infinite.
What is the order of an element of a group?
The order of a group is the same as its cardinality - i.e. the number of elements the set contains. The order of a particular element is the order of the (cyclic) group generated by that element - i.e. the order of the group {...a-4, a-3, a-2, a-1, e, a, a2, a3, a4...}. If these powers do not go on forever, it will have a finite order; otherwise the order will be infinite.
What is the order of grouping?
The order of a group is the same as its cardinality - i.e. the number of elements the set contains. The order of a particular element is the order of the (cyclic) group generated by that element - i.e. the order of the group {...a-4, a-3, a-2, a-1, e, a, a2, a3, a4...}. If these powers do not go on forever, it will have a finite order; otherwise the order will be infinite.
What is the order of the cyclic group mean?
The order of a cyclic group is the number of distinct elements in the group. It is also the smallest power, k, such that xk = i for all elements x in the group (i is the identity).
How do you find the order a factor group?
Let G be a finite group and H be a normal subgroup. G/H is the set of all co-sets of H forming a group known as factor group. By Lagrange's theorem the number of cosests (denoted by (G:H)) of H under G is |G|/|H|.
Is every group whose order is less than or equal to 4 a cyclic group?
Yes. The only group of order 1 is the trivial group containing only the identity element. All groups of orders 2 or 3 are cyclic since 2 and 3 are both prime numbers. Therefore, any group of order less than or equal to four must be a cyclic group.
Prove that a group of order 5 must be cyclic?
There's a theorem to the effect that every group of prime order is cyclic. Since 5 is prime, the assertion in the question follows from the said theorem.
A cyclic group of length 2 is called identity?
A cyclic group of order two looks like this.It has two elements e and x such that ex = xe = x and e2 = x2 = e.So it is clear how it relates to the identity.In a cyclic group of order 2, every element is its own inverse.
Let G be a cyclic group of order 8 then how many of the elements of G are generators of this group?
Four of them.
