Group Theory Concepts Quiz

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Questions and Answers

What is the result of the equation $o(x) = p_i m_i$ when $m_i = 0$?

  • $o(x) = 0$
  • $o(x) = 1$ (correct)
  • $o(x) = p_i$
  • $o(x) = p_i m_i$

When $x$ is an element of $H_i$, then $o(x)$ is equal to the order of $H_i$.

True (A)

What does $H_i igcap H_1 H_2 eq ext{e}$ imply?

It suggests that their intersection contains elements other than the identity element.

In the expression $x = (h_1 h_2 ... h_{i-1} h_{i+1} ... h_r)$, $h_t$ is the _____ element.

<p>identity</p> Signup and view all the answers

Match the symbols with their meanings:

<p>$o(x)$ = Order of element x $e$ = Identity element $H_i$ = Subgroup containing element x $m_i$ = Multiplicity of pi in factorization</p> Signup and view all the answers

Which of the following statements is true regarding the identity element in a group?

<p>The identity element is always unique. (D)</p> Signup and view all the answers

In an Abelian group, the operation is commutative.

<p>True (A)</p> Signup and view all the answers

What is a subgroup of a group G?

<p>A non-empty subset H of G that is itself a group with the same binary operation.</p> Signup and view all the answers

A group with infinite elements is called an __________ group.

<p>infinite</p> Signup and view all the answers

Match each term with its corresponding description:

<p>Normal Subgroup = Na = aN for all a in G Proper Subgroup = A subgroup that is not equal to G or {e} Coset = Set formed by Ha = {ha : h in H} Finite Group = A group with a limited number of elements</p> Signup and view all the answers

Which statement is true regarding the cancellation laws in group theory?

<p>If ab = ac, then b = c. (A)</p> Signup and view all the answers

All elements in a group must have unique inverses.

<p>True (A)</p> Signup and view all the answers

The sets Ha and aH are called __________ of a subgroup H in G.

<p>cosets</p> Signup and view all the answers

What is the relationship between the orders of the groups HxK and HxKx−1?

<p>o(HxK) = o(HxKx−1) (C)</p> Signup and view all the answers

If K is a subgroup of G, then xKx−1 is not a subgroup of G.

<p>False (B)</p> Signup and view all the answers

What is the highest power of p such that $p^n$ divides the order of G?

<p>n</p> Signup and view all the answers

According to Lagrange’s Theorem, o(H) o(H ∩ xKx−1) = ______.

<p>o(H ∩ xKx−1)</p> Signup and view all the answers

Match the following terms with their definitions:

<p>H = A Sylow p-subgroup of G K = Another Sylow p-subgroup of G n = The highest power of p dividing the order of G o(H) = The order of the subgroup H</p> Signup and view all the answers

What can be inferred if H and K are two Sylow p-subgroups of G?

<p>H and K are conjugate in G (D)</p> Signup and view all the answers

If o(H) = o(K) = p^n, then H and K must be equal.

<p>False (B)</p> Signup and view all the answers

What does the notation $xKx^{-1}$ signify in group theory?

<p>Conjugation of subgroup K by element x</p> Signup and view all the answers

What condition must hold for a subgroup to exist in G when considering the order o(G')?

<p>o(G') must be less than o(G) and pk divides o(G') (D)</p> Signup and view all the answers

If pm does not divide the order of any proper subgroup H of G, then pm divides o(G).

<p>True (A)</p> Signup and view all the answers

What theorem is applied to deduce the existence of an element a in Z(G) such that a^p = e?

<p>Cauchy Theorem for finite abelian groups</p> Signup and view all the answers

The cyclic subgroup generated by an element a is denoted as K = < a > = {a, a 2 , a 3 ,..., a ______}

<p>a^p</p> Signup and view all the answers

If $o(G) = pq$, where $p$ and $q$ are distinct primes and $p < q$, what can be deduced about the structure of $G$?

<p>G is cyclic. (B)</p> Signup and view all the answers

Match the following concepts with their definitions:

<p>o(G) = Order of group G Z(G) = Center of group G K = Cyclic subgroup generated by element a N(a) = Normal subgroup containing element a</p> Signup and view all the answers

The normalizer $N(H igcap K)$ is equal to the group $G$ if and only if $H$ is normal in $G$.

<p>True (A)</p> Signup and view all the answers

What does the class-equation for G describe?

<p>The relationship between the order of G and its center (B)</p> Signup and view all the answers

What is the condition for $N(H igcap K)$ to equal the entire group $G$?

<p>o(N(H ∩ K)) = o(G)</p> Signup and view all the answers

If $o(N(H igcap K)) = 108$, it follows that $G$ is __________.

<p>not simple</p> Signup and view all the answers

Every subgroup of Z(G) is a normal subgroup of G.

<p>True (A)</p> Signup and view all the answers

Match the Sylow theorem notations with their meanings:

<p>$n_p$ = Number of Sylow p-subgroups $n_q$ = Number of Sylow q-subgroups $H$ = Unique Sylow p-subgroup $K$ = Unique Sylow q-subgroup</p> Signup and view all the answers

In case I, what is assumed about the order of a subgroup H of G?

<p>pm divides o(H)</p> Signup and view all the answers

What condition leads to a contradiction when analyzing the number of Sylow $p$-subgroups?

<p>If $1 + kp = q$. (A)</p> Signup and view all the answers

The Sylow third theorem implies that a group with a unique Sylow subgroup is guaranteed to be abelian.

<p>False (B)</p> Signup and view all the answers

What can be concluded if $o(H) = p$ and $H$ is unique in $G$?

<p>H is normal in G.</p> Signup and view all the answers

Which condition must be satisfied for G to be considered an internal direct product of its Sylow subgroups?

<p>The intersection of any subgroup with the product of the others must be the identity. (C)</p> Signup and view all the answers

Every subgroup of an abelian group is normal in that group.

<p>True (A)</p> Signup and view all the answers

What is the identity element denoted as in group theory?

<p>e</p> Signup and view all the answers

If o(H_i) = p_i^{n_i}, then the order of the subgroup H_i is a power of the prime number _______.

<p>p_i</p> Signup and view all the answers

Match the concepts with their definitions:

<p>Normal subgroup = A subgroup that is invariant under conjugation by any element of the group Sylow subgroup = A maximal p-subgroup of a group Internal direct product = A product of subgroups where each pair of distinct subgroups intersects trivially Abelian group = A group where the group operation is commutative</p> Signup and view all the answers

In proving G is an internal direct product, which of the following is not required?

<p>G must contain exactly one Sylow subgroup for each prime factor. (D)</p> Signup and view all the answers

The equation x = h1h2...hi-1hi+1...hr implies that x is an element of Hi for any i.

<p>False (B)</p> Signup and view all the answers

What is the significance of the notation P_j for j ≠ i in the context of Sylow subgroups?

<p>It indicates that the subgroup order is a power of the prime number p_j.</p> Signup and view all the answers

Flashcards

Abelian group

A group where the order of operations doesn't matter. For all elements 'a' and 'b' in the group, 'ab' is equal to 'ba'.

Identity Element

The unique element in a group that leaves other elements unchanged when combined using the group's operation.

Inverse Element

For every element 'a' in a group, there is a unique element 'a⁻¹' such that 'a * a⁻¹' equals the identity element.

Subgroup

A subset of a group that is itself a group under the same operation.

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Right coset

The set of all elements obtained by multiplying each element of a subgroup 'H' by a fixed element 'a' from the group 'G'.

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Normal Subgroup

A subgroup 'N' where left and right cosets are the same for all elements.

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Order of a group

The number of elements in a finite group. An infinite group has an unlimited number of elements.

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Left coset

A set of elements obtained by multiplying each element of subgroup 'H' by a fixed element 'a' on the left, denoted as 'aH'.

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Theorem

A mathematical statement that is proven to be true in all cases.

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Case

A specific instance where the theorem applies.

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Order of a group (o(G))

The number of elements in a group.

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Center of a group (Z(G))

The set of elements in a group that commute with all elements in the group.

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Group

A set of elements that satisfy the group axioms.

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Normal subgroup (N(a)  G)

A subgroup of a group that is invariant under conjugation by elements of the group.

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Element raised to a power equals the identity element (a^p = e)

An element in a group raised to a power equals the identity element.

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Order of an Element

The order of an element in a group is the smallest positive integer 'n' such that 'a^n' equals the identity element. If no such 'n' exists, the order is infinite.

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Sylow p-subgroup

A Sylow p-subgroup of a group 'G' is a maximal subgroup of 'G' whose order is the highest power of 'p' that divides the order of 'G'.

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Product of subgroups (HxK)

If H and K are two subgroups of a group G, then the product of H and K is the set of all elements obtained by multiplying an element from H with an element from K.

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Intersection of subgroups (H ∩ K)

The intersection of two sets is the set of elements that are common to both sets. In the context of groups, the intersection of two subgroups is the set of elements that belong to both subgroups.

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Conjugate of a subgroup (xKx⁻¹)

A conjugate of a subgroup 'K' in a group 'G' is a subgroup obtained by multiplying 'K' by an element 'x' from the group and then by its inverse, denoted as 'xKx⁻¹'.

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Lagrange's Theorem

Lagrange's Theorem states that the order of any subgroup of a finite group must divide the order of the group.

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Conjugate subgroups

Two subgroups 'H' and 'K' of a group 'G' are called conjugate if there exists an element 'x' in 'G' such that 'H = xKx⁻¹'.

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Sylow's Second Theorem

Sylow's Second Theorem states that any two Sylow p-subgroups of a finite group 'G' are conjugate in 'G'.

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Internal Direct Product

A group that is formed from the combination of two or more normal subgroups, where the intersection of any two subgroups is the identity element.

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Normalizer Property for Intersection

An element 'x' belongs to the normalizer of the intersection of subgroups 'H' and 'K' if it satisfies the property: (H  K)x = x(H  K).

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Normalizer Definition

The normalizer of a set 'S' in a group 'G' is the set of all elements 'g' in 'G' that 'normalize' 'S', meaning: gSg⁻¹ = S.

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Order Inequality in Normalizers

The order of the normalizer of (H  K) is greater than or equal to the order of HK, which is the product of the orders of 'H' and 'K' divided by the order of their intersection (H  K).

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Lagrange's Theorem for Normalizers

The order of the normalizer of (H  K) is a divisor of the order of the group 'G'.

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Normal Subgroup Condition

If the order of the normalizer of (H  K) is equal to the order of the group 'G', then the normalizer is the whole group, which implies that (H  K) is a normal subgroup in 'G'.

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Simple Group Definition

A group is called simple if it has no non-trivial normal subgroups (other than the trivial subgroup containing only the identity element and the group itself).

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Cyclic Group Condition

For a group 'G' of order 'pq', where 'p' and 'q' are distinct primes with 'p' less than 'q' and 'p' not dividing 'q-1', then 'G' is a cyclic group.

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Sylow Third Theorem

The number of Sylow p-subgroups in a group 'G' is of the form 1 + kp, where 'k' is an integer, and this number divides the order of the group 'G'.

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Order of an element (o(x))

The order of an element 'x' in a group is the smallest positive integer 'n' such that x raised to the power of 'n' equals the identity element (x^n = e).

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Intersection of subgroups (H ∩ H1H2...Hi-1Hi+1...Hr = {e})

The intersection of a subgroup H and the product of all other subgroups (except H) within a larger group G results in only the identity element (e). This means the subgroups are essentially independent of each other.

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Order of element is a multiple of subgroup order (o(x) o(H))

The order of an element 'x' is a multiple of the order of its subgroup H. This means that if you multiply 'x' by itself enough times to get to the identity element, you'll also have gone through all the elements of H.

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Product of subgroup orders excluding Hi (o(x) = p1^n1 * p2^n2 * ... * pi-1^n(i-1) * pi+1^n(i+1) * ... * pr^nr)

The order of an element 'x' is equal to the product of the orders of its subgroups (excluding the subgroup 'H') for all subgroups 'Hi' in the larger group 'G'.

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Order of element expressed as a power of subgroup order (o(x) = pimi, where 0 <= mi <= ni)

The order of an element 'x' within a group 'G' can be expressed as a power of the prime order of each subgroup 'Hi'.

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Study Notes

Course Information

  • Course: Abstract Algebra
  • Paper Code: 20MAT21C1
  • Semester: 1
  • University: Maharshi Dayanand University, Rohtak

Course Outcomes

  • Students will be able to apply group theoretic reasoning to group actions.
  • Students will learn properties and analysis of solvable and nilpotent groups, Noetherian and Artinian modules and rings.
  • Students will apply Sylow's theorems to analyze finite groups.
  • Students will use various canonical types of groups and rings.
  • Students will analyze composition series.

Course Content

  • Section I: Conjugates and centralizers in Sn, p-groups, Group actions, Counting orbits. Sylow subgroups, Sylow theorems, Applications of Sylow theorems, Description of groups of order p² and pq, Survey of groups up to order 15.
  • Section II: Normal and subnormal series, Solvable series, Derived series, Solvable groups, Solvability of Sn, Central series, Nilpotent groups, Equivalent conditions for a finite group to be nilpotent, Upper and lower central series. Composition series, Zassenhaus lemma, Jordan-Holder theorem.
  • Section III: Modules, Cyclic modules, Simple and semi-simple modules, Schur lemma, Free modules, Torsion modules, Torsion-free modules, Torsion part of a module, Modules over principal ideal domain, and its applications to finitely generated abelian groups.
  • Section IV: Noetherian and Artinian modules, Modules of finite length, Noetherian and Artinian rings, Hilbert basis theorem. Properties of Jacobson radical.
  • Luther, I.S., Passi, I.B.S., Algebra, Vol I: Groups, Vol III: Modules, Narosa Publishing House.
  • Lanski, C., Concepts in Abstract Algebra, American Mathematical Society.
  • Sahai, V., Bist, V., Algebra, Narosa Publishing House.
  • Malik, D.S., Mordenson, J.N., and Sen, M.K., Fundamentals of Abstract Algebra, McGraw Hill.
  • Bhattacharya, P.B., Jain, S.K., and Nagpaul, S.R., Basic Abstract Algebra.
  • Musili, C., Introduction to Rings and Modules, Narosa.
  • Jacobson, N., Basic Algebra, Vol I & II, W.H Freeman
  • Artin, M., Algebra, Prentice-Hall of India.
  • Macdonald, I. D., The Theory of Groups, Clarendon Press.

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