Solved assignment for IGNOU MMT-003 for the 2024 session.

IGNOU MMT-003 Solved Assignment 2024 | M.Sc. MACS

Solved By – Narendra Kr. Sharma – M.Sc (Mathematics Honors) – Delhi University

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IGNOU MMT-003 Assignment Question Paper 2024

mmt-003-assignment-question-paper-1f02de37-022a-430d-b961-44d586763fd8

mmt-003-assignment-question-paper-1f02de37-022a-430d-b961-44d586763fd8

  1. Which of the following statements are true and which are false? Give reasons for your answer.
    (a) If a finite group G G GGG acts on a finite set S S SSS, then G s 1 = G s 2 G s 1 = G s 2 G_(s_(1))=G_(s_(2))G_{s_1}=G_{s_2}Gs1=Gs2 for all s 1 , s 2 X s 1 , s 2 X s_(1),s_(2)in Xs_1, s_2 \in Xs1,s2X.
    (b) There are exactly 8 elements of order 3 in S 4 S 4 S_(4)S_4S4.
    (c) If F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53), then [ F : Q ] = 8 [ F : Q ] = 8 [F:Q]=8[F: \mathbb{Q}]=8[F:Q]=8.
    (d) F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5).
    (e) For any α F 2 5 , α 1 , F 2 5 = F 2 [ α ] α F 2 5 , α 1 , F 2 5 = F 2 [ α ] alpha inF_(2^(5))^(**),alpha!=1,F_(2^(5))=F_(2)[alpha]\alpha \in \mathbb{F}_{2^5}^*, \alpha \neq 1, \mathbb{F}_{2^5}=\mathbb{F}_2[\alpha]αF25,α1,F25=F2[α].
  2. (a) Consider the natural action of G L 2 ( R ) G L 2 ( R ) GL_(2)(R)G L_2(\mathbb{R})GL2(R) on M 2 ( R ) M 2 ( R ) M_(2)(R)\mathbf{M}_2(\mathbb{R})M2(R), the set of 2 × 2 2 × 2 2xx22 \times 22×2 real matrices, by left multiplication.
    (i) Under this action, if det ( x ) 0 det ( x ) 0 det(x)!=0\operatorname{det}(\mathbf{x}) \neq \mathbf{0}det(x)0, show that the stabiliser of x M 2 ( R ) x M 2 ( R ) xinM_(2)(R)\mathbf{x} \in M_2(\mathbb{R})xM2(R) is { I } { I } {I}\{\mathbf{I}\}{I}, where I I I\mathbf{I}I is the 2 × 2 2 × 2 2xx22 \times 22×2 identity matrix.
    (ii) Suppose that det ( x ) = 0 det ( x ) = 0 det(x)=0\operatorname{det}(\mathbf{x})=\mathbf{0}det(x)=0 in the remaining parts of this exercise. We will show that the stabiliser of x x x\mathbf{x}x is infinite. If x = 0 x = 0 x=0\mathbf{x}=\mathbf{0}x=0, the stabiliser of x x x\mathbf{x}x is G L 2 ( R ) G L 2 ( R ) GL_(2)(R)G L_2(\mathbb{R})GL2(R). So suppose x 0 x 0 x!=0\mathbf{x} \neq \mathbf{0}x0. Let us write x = [ a c b d ] x = a      c b      d x=[[a,c],[b,d]]\mathbf{x}=\left[\begin{array}{ll}a & c \\ b & d\end{array}\right]x=[acbd]. Then, [ a b ] = λ [ c d ] a b = λ c d [[a],[b]]=lambda[[c],[d]]\left[\begin{array}{l}a \\ b\end{array}\right]=\lambda\left[\begin{array}{l}c \\ d\end{array}\right][ab]=λ[cd] for non-zero λ R λ R lambda inR\lambda \in \mathbb{R}λR. Why ?
    (iii) Let [ a b ] a b [[a^(‘)],[b^(‘)]]\left[\begin{array}{l}a^{\prime} \\ b^{\prime}\end{array}\right][ab] be a vector that is not a scalar multiple of [ a b ] a b [[a],[b]]\left[\begin{array}{l}a \\ b\end{array}\right][ab]. Show that there is a matrix b = b = b=\mathbf{b}=b= [ u v w z ] u      v w      z [[u,v],[w,z]]\left[\begin{array}{ll}u & v \\ w & z\end{array}\right][uvwz] such that b [ a b ] = 0 b a b = 0 b[[a],[b]]=0\mathbf{b}\left[\begin{array}{l}a \\ b\end{array}\right]=\mathbf{0}b[ab]=0 and b [ a b ] = α [ a b ] b a b = α a b b[[a^(‘)],[b^(‘)]]=alpha[[a^(‘)],[b^(‘)]]\mathbf{b}\left[\begin{array}{l}a^{\prime} \\ b^{\prime}\end{array}\right]=\alpha\left[\begin{array}{l}a^{\prime} \\ b^{\prime}\end{array}\right]b[ab]=α[ab].(Hint: Set up two sets of simultaneous equations in two unknowns and argue why they have a solution.)
    (iv) Check that I b I b I-b\mathbf{I}-\mathbf{b}Ib is in the stabiliser of x x x\mathbf{x}x. Also, show that there are infinitely many choices of α α alpha\alphaα for which I b I b I-b\mathbf{I}-\mathbf{b}Ib is invertible.
    (b) Let H H HHH be a finite group and, for some prime p p ppp, let P P PPP be a p-Sylow subgroup of H H HHH which is normal in H H HHH. Suppose H H HHH is normal in K K KKK, where K K KKK is a finite group. Then, show that P P PPP is normal in K K KKK.
    (c) Find the elementary divisors and invariant factors of Z 8 × Z 12 × Z 15 Z 8 × Z 12 × Z 15 Z_(8)xxZ_(12)xxZ_(15)\mathbb{Z}_8 \times \mathbb{Z}_{12} \times \mathbb{Z}_{15}Z8×Z12×Z15.
  3. Describe the set of primes p p ppp for which x 2 11 x 2 11 x^(2)-11x^2-11x211 splits into linear factors over Z p Z p Z_(p)\mathbb{Z}_pZp.
  4. (a) Determine, up to isomorphism, all the finite groups with exactly 2 conjugacy classes.
    (b) Is there a finite group with class equation 1 + 1 + 2 + 2 + 2 + 2 + 2 + 2 1 + 1 + 2 + 2 + 2 + 2 + 2 + 2 1+1+2+2+2+2+2+21+1+2+2+2+2+2+21+1+2+2+2+2+2+2 ?
    (c) Compute the following:
    a) ( 173 211 ) 173 211 ((173)/(211))\left(\frac{173}{211}\right)(173211)
    b) ( 167 239 ) 167 239 ((167)/(239))\left(\frac{167}{239}\right)(167239).
  5. (a) Let F ( α ) F ( α ) F(alpha)F(\alpha)F(α) be a finite extension F F FFF of odd degree(greater than 1). Show that F ( α 2 ) = F ( α ) F α 2 = F ( α ) F(alpha^(2))=F(alpha)F\left(\alpha^2\right)=F(\alpha)F(α2)=F(α).
    (b) Let F K F K F sub KF \subset KFK and let α , β K α , β K alpha,beta in K\alpha, \beta \in Kα,βK be algebraic over F F F\mathrm{F}F of degree m m m\mathrm{m}m and n n n\mathrm{n}n, respectively. Show that [ F ( α , β ) : F ] m n [ F ( α , β ) : F ] m n [F(alpha,beta):F] <= mn[F(\alpha, \beta): F] \leq m n[F(α,β):F]mn. What can you say about [ F ( α , β ) : F ] [ F ( α , β ) : F ] [F(alpha,beta):F][F(\alpha, \beta): F][F(α,β):F] if m m m\mathrm{m}m and n n n\mathrm{n}n are coprime?
    (c) Find [ Q ( 2 3 , ω ) : Q ] [ Q ( 2 3 , ω ) : Q ] [Q(root(3)(2),omega):Q][\mathbb{Q}(\sqrt[3]{2}, \omega): \mathbb{Q}][Q(23,ω):Q] where ω 3 = 1 , ω 1 ω 3 = 1 , ω 1 omega^(3)=1,omega!=1\omega^3=1, \omega \neq 1ω3=1,ω1.
  6. (a) If char ( F ) 2 char ( F ) 2 char(F)!=2\operatorname{char}(F) \neq 2char(F)2, show that a polynomial a x 2 + b x + c a x 2 + b x + c ax^(2)+bx+ca x^2+b x+cax2+bx+c is irreducible iff b 2 4 a c F 2 b 2 4 a c F 2 b^(2)-4ac!inF^(**2)b^2-4 a c \notin \mathbb{F}^{* 2}b24acF2 where F 2 F 2 F^(**2)\mathbb{F}^{* 2}F2 is the group of squares in F F F^(**)\mathbb{F}^*F.
    (b) By looking at the factorisation of x 9 x F 3 [ x ] x 9 x F 3 [ x ] x^(9)-x inF_(3)[x]x^9-x \in \mathbb{F}_3[x]x9xF3[x] guess the number of irreducible polynomials of degree 2 over F 3 F 3 F_(3)\mathbb{F}_3F3. Find all the irreducible polynomials of degree 2 over F 3 F 3 F_(3)\mathbb{F}_3F3.
    (c) If F F F\mathbb{F}F is a finite field show that there is always an irreducible polynomial of the form x 3 x + a x 3 x + a x^(3)-x+ax^3-x+ax3x+a where a F a F a in Fa \in FaF.(Hint: Show that x x 3 x x x 3 x x|->x^(3)-xx \mapsto x^3-xxx3x is not a surjective map.)
  7. (a) Suppose that M = [ A B C D ] M = A      B C      D M=[[A,B],[C,D]]M=\left[\begin{array}{ll}A & B \\ C & D\end{array}\right]M=[ABCD] is 2 n × 2 n 2 n × 2 n 2n xx2n2 n \times 2 n2n×2n matrix where A , B , C A , B , C A,B,CA, B, CA,B,C and D D DDD are n × n n × n n xx nn \times nn×n matrices. Show that M M MMM is symplectic if and only if the following conditions are satisfied:
A t D C t B = I A t C C t A = 0 B t D D t B = 0 A t D C t B = I A t C C t A = 0 B t D D t B = 0 {:[A^(t)D-C^(t)B=I],[A^(t)C-C^(t)A=0],[B^(t)D-D^(t)B=0]:}\begin{aligned} & A^t D-C^t B=\mathbf{I} \\ & A^t C-C^t A=\mathbf{0} \\ & B^t D-D^t B=\mathbf{0} \end{aligned}AtDCtB=IAtCCtA=0BtDDtB=0
(Hint: Use block matrix multiplication.)
Also, check that the matrix [ 0 A A 0 ] 0 A A 0 [[0,-A],[A,0]]\left[\begin{array}{cc}\mathbf{0} & -A \\ A & \mathbf{0}\end{array}\right][0AA0], where A A AAA is a n × n n × n n xx nn \times nn×n orthogonal matrix, is a symplectic matrix.
(b) The aim of this exercise is to show that S P 2 ( R ) S P 2 ( R ) SP_(2)(R)S P_2(\mathbb{R})SP2(R) acts transitively on R 2 { 0 } R 2 { 0 } R^(2)\\{0}\mathbb{R}^2 \backslash\{0\}R2{0}.
(c) Show that
(i) Show that a matrix [ a b c d ] G L 2 ( R ) a      b c      d G L 2 ( R ) [[a,b],[c,d]]in GL_(2)(R)\left[\begin{array}{ll}a & b \\ c & d\end{array}\right] \in G L_2(\mathbb{R})[abcd]GL2(R) is symplectic if and only if a d b c = 1 a d b c = 1 ad-bc=1a d-b c=1adbc=1.
(ii) Show that, to prove that S P 2 ( R ) S P 2 ( R ) SP_(2)(R)\mathrm{SP}_2(\mathbb{R})SP2(R) acts transitively on G L 2 ( R ) G L 2 ( R ) GL_(2)(R)G L_2(\mathbb{R})GL2(R), it is enough to show that, for any vector [ a b ] 0 R 2 a b 0 R 2 [[a],[b]]!=0inR^(2)\left[\begin{array}{l}a \\ b\end{array}\right] \neq \mathbf{0} \in \mathbb{R}^2[ab]0R2, there is a 2 × 2 2 × 2 2xx22 \times 22×2 symplectic matrix with [ a b ] a b [[a],[b]]\left[\begin{array}{l}a \\ b\end{array}\right][ab] as the first column. (Hint: For any matrix A A AAA, what is A [ 1 0 ] A 1 0 A[[1],[0]]A\left[\begin{array}{l}1 \\ 0\end{array}\right]A[10] ?)
(iii) Complete the proof by showing that, given any non-zero vector [ a b ] a b [[a],[b]]\left[\begin{array}{l}a \\ b\end{array}\right][ab], there is always a non-zero vector [ a b ] a b [[a^(‘)],[b^(‘)]]\left[\begin{array}{l}a^{\prime} \\ b^{\prime}\end{array}\right][ab] such that [ a a b b ] a      a b      b [[a,a^(‘)],[b,b^(‘)]]\left[\begin{array}{ll}a & a^{\prime} \\ b & b^{\prime}\end{array}\right][aabb] is symplectic.
8. In this exercise, we ask you to find the Sylow p p ppp-subgroups of the dihedral group
D n = x , y : x n , y 2 , y x y x , n N , n 2 . D n = x , y : x n , y 2 , y x y x , n N , n 2 . D_(n)=(:x,y:x^(n),y^(2),yxyx:),n inN,n >= 2.D_n=\left\langle x, y: x^n, y^2, y x y x\right\rangle, n \in \mathbb{N}, n \geq 2 .Dn=x,y:xn,y2,yxyx,nN,n2.
(a) Let p p ppp be an odd prime that divides n , n = p r l , p l n , n = p r l , p l n,n=p^(r)l,p∤ln, n=p^r l, p \nmid ln,n=prl,pl. Suppose C = x l C = x l C=(:x^(l):)C=\left\langle x^l\right\rangleC=xl. Show that C C CCC is the unique Sylow p p ppp-subgroup of D n D n D_(n)D_nDn.
(b) Prove the relation
y i x j y k x l = { y i x j + l if k is even y i + k x l j if k is odd. y i x j y k x l = y i x j + l      if k is even y i + k x l j      if k is odd. y^(i)x^(j)y^(k)x^(l)={[y^(i)x^(j+l),” if “k” is even “],[y^(i+k)x^(l-j),” if “k” is odd. “]:}y^i x^j y^k x^l= \begin{cases}y^i x^{j+l} & \text { if } \mathrm{k} \text { is even } \\ y^{i+k} x^{l-j} & \text { if } \mathrm{k} \text { is odd. }\end{cases}yixjykxl={yixj+l if k is even yi+kxlj if k is odd.
Further, find all the elements of order 2 in D n D n D_(n)D_nDn.
(c) Find all the Sylow 2-subgroups of D n D n D_(n)D_nDn when n n nnn is odd. Describe them in terms of x x xxx and y y yyy.
(d) Suppose n n nnn is even, n = 2 k m n = 2 k m n=2^(k)mn=2^k mn=2km, where 2 m , k 2 2 m , k 2 2∤m,k >= 22 \nmid m, k \geq 22m,k2. Let N = x m N = x m N=(:x^(m):)N=\left\langle x^m\right\rangleN=xm and H = y H = y H=(:y:)H=\langle y\rangleH=y. Show that H N H N HNH NHN is a subgroup of D n D n D_(n)D_nDn. What is its order?
(e) Suppose n n nnn is as in the previous part. Find all the Sylow 2-supgroups of D n D n D_(n)D_nDn. Describe them in terms of x x xxx and y y yyy.
9. (a) Let G = a , b a 2 , b 3 , a b a 1 b 1 G = a , b a 2 , b 3 , a b a 1 b 1 G=(:a,b∣a^(2),b^(3),aba^(-1)b^(-1):)G=\left\langle a, b \mid a^2, b^3, a b a^{-1} b^{-1}\right\rangleG=a,ba2,b3,aba1b1. Show that G G GGG is the cyclic group of order six.
(b) Solve the following set of congruences:
x 2 ( mod 17 ) 3 x 4 ( mod 19 ) x 7 ( mod 23 ) x      2           ( mod 17 ) 3 x      4      ( mod 19 ) x      7           ( mod 23 ) {:[x,-=2,,(mod 17)],[3x,-=4,(mod 19)],[x,-=7,,(mod 23)]:}\begin{array}{rlrl} x & \equiv 2 & & (\bmod 17) \\ 3 x & \equiv 4 & (\bmod 19) \\ x & \equiv 7 & & (\bmod 23) \end{array}x2(mod17)3x4(mod19)x7(mod23)
(c) Show that Q ( 19 ) Q ( 19 ) Q(sqrt(-19))\mathbb{Q}(\sqrt{-19})Q(19) is not a UFD by giving two different factorisations of 20 .
\(Sin^2\left(\theta \:\right)+Cos^2\left(\theta \right)=1\)

MMT-003 Sample Solution 2024

mmt-003-solved-assignment-2024-ss-020cab3d-1c01-486f-9bdf-7506d86b97ee

mmt-003-solved-assignment-2024-ss-020cab3d-1c01-486f-9bdf-7506d86b97ee

MMT-003 Solved Assignment 2024
  1. Which of the following statements are true and which are false? Give reasons for your answer.
    (a) If a finite group G G GGG acts on a finite set S S SSS, then G s 1 = G s 2 G s 1 = G s 2 G_(s_(1))=G_(s_(2))G_{s_1}=G_{s_2}Gs1=Gs2 for all s 1 , s 2 X s 1 , s 2 X s_(1),s_(2)in Xs_1, s_2 \in Xs1,s2X.
Answer:
The statement "If a finite group G G GGG acts on a finite set S S SSS, then G s 1 = G s 2 G s 1 = G s 2 G_(s_(1))=G_(s_(2))G_{s_1}=G_{s_2}Gs1=Gs2 for all s 1 , s 2 S s 1 , s 2 S s_(1),s_(2)in Ss_1, s_2 \in Ss1,s2S" is false. Here, G s 1 G s 1 G_(s_(1))G_{s_1}Gs1 and G s 2 G s 2 G_(s_(2))G_{s_2}Gs2 denote the stabilizer subgroups of s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2 in S S SSS, respectively. The stabilizer subgroup G s G s G_(s)G_sGs of an element s S s S s in Ss \in SsS is defined as the set of all elements in G G GGG that fix s s sss, i.e., G s = { g G g s = s } G s = { g G g s = s } G_(s)={g in G∣g*s=s}G_s = \{g \in G \mid g \cdot s = s\}Gs={gGgs=s}.
Justification/Proof:
The statement claims that for any two elements s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2 in the set S S SSS, their stabilizer subgroups in G G GGG are equal. This would mean that every element of G G GGG that fixes s 1 s 1 s_(1)s_1s1 also fixes s 2 s 2 s_(2)s_2s2 and vice versa. However, this is not necessarily true for all actions of G G GGG on S S SSS. The equality of stabilizers for all elements in S S SSS would imply a very rigid action, essentially saying that either the entire group fixes every element of S S SSS or that the action is trivial (where G G GGG acts on S S SSS in such a way that every element of G G GGG fixes every element of S S SSS).
Counterexample:
Consider the group G = { e , g } G = { e , g } G={e,g}G = \{e, g\}G={e,g} where e e eee is the identity element and g g ggg is an element of order 2 (meaning g 2 = e g 2 = e g^(2)=eg^2 = eg2=e), acting on the set S = { s 1 , s 2 } S = { s 1 , s 2 } S={s_(1),s_(2)}S = \{s_1, s_2\}S={s1,s2} with two elements. Define the action of G G GGG on S S SSS as follows:
  • e e eee fixes both s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2 (as it must, being the identity).
  • g g ggg swaps s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2, i.e., g s 1 = s 2 g s 1 = s 2 g*s_(1)=s_(2)g \cdot s_1 = s_2gs1=s2 and g s 2 = s 1 g s 2 = s 1 g*s_(2)=s_(1)g \cdot s_2 = s_1gs2=s1.
For this action, we have:
  • G s 1 = { e } G s 1 = { e } G_(s_(1))={e}G_{s_1} = \{e\}Gs1={e} because only the identity element fixes s 1 s 1 s_(1)s_1s1.
  • G s 2 = { e } G s 2 = { e } G_(s_(2))={e}G_{s_2} = \{e\}Gs2={e} because only the identity element fixes s 2 s 2 s_(2)s_2s2.
In this specific example, G s 1 G s 1 G_(s_(1))G_{s_1}Gs1 and G s 2 G s 2 G_(s_(2))G_{s_2}Gs2 happen to be equal because the non-identity element of G G GGG does not fix either of the elements of S S SSS but rather swaps them. However, the action of g g ggg clearly differentiates s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2, showing that the nature of the action can lead to different behaviors for different elements of S S SSS, and it’s easy to construct examples where G s 1 G s 2 G s 1 G s 2 G_(s_(1))!=G_(s_(2))G_{s_1} \neq G_{s_2}Gs1Gs2 by adjusting the action.
For a more direct counterexample to the statement, consider a group G G GGG acting on a set S = { s 1 , s 2 , s 3 } S = { s 1 , s 2 , s 3 } S={s_(1),s_(2),s_(3)}S = \{s_1, s_2, s_3\}S={s1,s2,s3} where G G GGG fixes s 1 s 1 s_(1)s_1s1 and s 2 s 2 s_(2)s_2s2 but not s 3 s 3 s_(3)s_3s3, or any scenario where the action is not uniform across all elements of S S SSS. This shows that the original statement is false.
(b) There are exactly 8 elements of order 3 in S 4 S 4 S_(4)S_4S4.
Answer:
To determine the truth of the statement "There are exactly 8 elements of order 3 in S 4 S 4 S_(4)S_4S4," we need to understand the structure of the symmetric group S 4 S 4 S_(4)S_4S4 and the concept of an element’s order.
Background:
  • The symmetric group S 4 S 4 S_(4)S_4S4 consists of all permutations of four elements, with a total of 4 ! = 24 4 ! = 24 4!=244! = 244!=24 elements.
  • The order of an element in a group is the smallest positive integer n n nnn such that the element raised to the n n nnnth power (under the group operation, which is composition in this case) equals the identity element. For permutations, this means repeating the permutation n n nnn times returns the set to its original order.
Analysis:
Elements of order 3 in S 4 S 4 S_(4)S_4S4 are those permutations that cycle three elements while leaving the fourth unchanged. These can be represented as 3-cycles, such as ( 123 ) ( 123 ) (123)(123)(123), which means that 1 goes to 2, 2 goes to 3, and 3 goes back to 1, with the fourth element (in this case, 4) remaining fixed.
To count the elements of order 3, we look for all possible 3-cycles within S 4 S 4 S_(4)S_4S4. A 3-cycle can be chosen by selecting 3 elements out of 4 to participate in the cycle, and the order in which these three elements are arranged matters (since ( 123 ) ( 123 ) (123)(123)(123) is different from ( 132 ) ( 132 ) (132)(132)(132), for example).
Counting 3-Cycles:
The number of ways to choose 3 elements out of 4 is given by the combination formula ( 4 3 ) ( 4 3 ) ((4)/(3))\binom{4}{3}(43). For each selection of 3 elements, there are 2 ways to arrange them into a cycle (since for any three distinct elements a a aaa, b b bbb, and c c ccc, there are exactly two 3-cycles: ( a b c ) ( a b c ) (abc)(abc)(abc) and ( a c b ) ( a c b ) (acb)(acb)(acb)).
Thus, the total number of 3-cycles (elements of order 3) in S 4 S 4 S_(4)S_4S4 is:
( 4 3 ) × 2 ( 4 3 ) × 2 ((4)/(3))xx2\binom{4}{3} \times 2(43)×2
Let’s calculate this value:
( 4 3 ) × 2 = 4 × 2 = 8 ( 4 3 ) × 2 = 4 × 2 = 8 ((4)/(3))xx2=4xx2=8\binom{4}{3} \times 2 = 4 \times 2 = 8(43)×2=4×2=8
After calculating, we find that there are indeed exactly 8 elements of order 3 in S 4 S 4 S_(4)S_4S4, which means the statement is true. Each of these elements is a permutation that cycles three of the four elements back to their original positions after three applications, which is the definition of having order 3.
(c) If F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53), then [ F : Q ] = 8 [ F : Q ] = 8 [F:Q]=8[F: \mathbb{Q}]=8[F:Q]=8.
Answer:
To evaluate the statement "If F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53), then [ F : Q ] = 8 [ F : Q ] = 8 [F:Q]=8[F: \mathbb{Q}]=8[F:Q]=8," we need to understand the concept of field extensions and the degree of an extension.
Background:
  • F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53) is a field extension of Q Q Q\mathbb{Q}Q that includes both 2 5 2 5 root(5)(2)\sqrt[5]{2}25 and 5 3 5 3 root(3)(5)\sqrt[3]{5}53.
  • The degree of the extension [ F : Q ] [ F : Q ] [F:Q][F: \mathbb{Q}][F:Q] is the dimension of F F FFF as a vector space over Q Q Q\mathbb{Q}Q.
  • The degree of a composite extension can be determined by the multiplicativity of degrees in tower extensions: if K L M K L M K sube L sube MK \subseteq L \subseteq MKLM are fields, then [ M : K ] = [ M : L ] [ L : K ] [ M : K ] = [ M : L ] [ L : K ] [M:K]=[M:L][L:K][M:K] = [M:L][L:K][M:K]=[M:L][L:K].
Analysis:
  1. Consider the extension Q ( 2 5 ) Q ( 2 5 ) Q(root(5)(2))\mathbb{Q}(\sqrt[5]{2})Q(25) over Q Q Q\mathbb{Q}Q. The minimal polynomial of 2 5 2 5 root(5)(2)\sqrt[5]{2}25 over Q Q Q\mathbb{Q}Q is x 5 2 x 5 2 x^(5)-2x^5 – 2x52, which is irreducible over Q Q Q\mathbb{Q}Q by Eisenstein’s criterion (with prime p = 2 p = 2 p=2p=2p=2). Thus, [ Q ( 2 5 ) : Q ] = 5 [ Q ( 2 5 ) : Q ] = 5 [Q(root(5)(2)):Q]=5[\mathbb{Q}(\sqrt[5]{2}):\mathbb{Q}] = 5[Q(25):Q]=5.
  2. Consider the extension Q ( 5 3 ) Q ( 5 3 ) Q(root(3)(5))\mathbb{Q}(\sqrt[3]{5})Q(53) over Q Q Q\mathbb{Q}Q. The minimal polynomial of 5 3 5 3 root(3)(5)\sqrt[3]{5}53 over Q Q Q\mathbb{Q}Q is x 3 5 x 3 5 x^(3)-5x^3 – 5x35, which is also irreducible over Q Q Q\mathbb{Q}Q by Eisenstein’s criterion (with prime p = 5 p = 5 p=5p=5p=5). Thus, [ Q ( 5 3 ) : Q ] = 3 [ Q ( 5 3 ) : Q ] = 3 [Q(root(3)(5)):Q]=3[\mathbb{Q}(\sqrt[3]{5}):\mathbb{Q}] = 3[Q(53):Q]=3.
  3. To find [ F : Q ] [ F : Q ] [F:Q][F: \mathbb{Q}][F:Q] where F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53), we need to consider how 2 5 2 5 root(5)(2)\sqrt[5]{2}25 and 5 3 5 3 root(3)(5)\sqrt[3]{5}53 interact within the extension. If these roots were to generate independent extensions (i.e., the extensions do not intersect in a way that reduces the overall degree), then we might expect the degree of F F FFF over Q Q Q\mathbb{Q}Q to be the product of the degrees of the individual extensions. However, the actual degree of the combined extension depends on the interaction between these two extensions.
Given that the degrees of the individual extensions are 5 and 3, respectively, and assuming no prior knowledge about a direct interaction that would reduce the combined degree, one might naively expect the degree of the combined extension to be 5 × 3 = 15 5 × 3 = 15 5xx3=155 \times 3 = 155×3=15. This is because the extensions are generated by roots of polynomials that are irreducible over Q Q Q\mathbb{Q}Q and do not immediately suggest a common field that would reduce the degree of the extension.
Conclusion:
The statement "If F = Q ( 2 5 , 5 3 ) F = Q ( 2 5 , 5 3 ) F=Q(root(5)(2),root(3)(5))F=\mathbb{Q}(\sqrt[5]{2}, \sqrt[3]{5})F=Q(25,53), then [ F : Q ] = 8 [ F : Q ] = 8 [F:Q]=8[F: \mathbb{Q}]=8[F:Q]=8" is false. Based on the analysis above, without specific interaction that would reduce the degree, the expected degree of the field extension F F FFF over Q Q Q\mathbb{Q}Q would naively be calculated as 15 15 151515, not 8 8 888, assuming independent extensions generated by 2 5 2 5 root(5)(2)\sqrt[5]{2}25 and 5 3 5 3 root(3)(5)\sqrt[3]{5}53. However, the actual degree calculation requires detailed knowledge of how these extensions interact, and in general, the degree of such a combined extension is not simply the product of the degrees if there’s a nontrivial intersection. But in this specific case, without evidence of such an intersection that would lower the degree to 8 8 888, the initial analysis suggests the statement is incorrect.
(d) F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5).
Answer:
To evaluate the statement " F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5)," we need to understand the structure of finite fields, specifically the field extensions of F 7 F 7 F_(7)\mathbf{F}_7F7, the finite field with 7 elements.
Background:
  • F 7 F 7 F_(7)\mathbf{F}_7F7 is the finite field with 7 elements, typically represented as { 0 , 1 , 2 , 3 , 4 , 5 , 6 } { 0 , 1 , 2 , 3 , 4 , 5 , 6 } {0,1,2,3,4,5,6}\{0, 1, 2, 3, 4, 5, 6\}{0,1,2,3,4,5,6} with arithmetic operations performed modulo 7.
  • F 7 ( 3 ) F 7 ( 3 ) F_(7)(sqrt3)\mathbf{F}_7(\sqrt{3})F7(3) denotes the smallest field extension of F 7 F 7 F_(7)\mathbf{F}_7F7 containing 3 3 sqrt3\sqrt{3}3, and similarly, F 7 ( 5 ) F 7 ( 5 ) F_(7)(sqrt5)\mathbf{F}_7(\sqrt{5})F7(5) denotes the smallest field extension of F 7 F 7 F_(7)\mathbf{F}_7F7 containing 5 5 sqrt5\sqrt{5}5.
  • In the context of finite fields, an element a a aaa is said to have a square root in F 7 F 7 F_(7)\mathbf{F}_7F7 if there exists an element b F 7 b F 7 b inF_(7)b \in \mathbf{F}_7bF7 such that b 2 a mod 7 b 2 a mod 7 b^(2)-=amod7b^2 \equiv a \mod 7b2amod7.
Analysis:
To determine whether F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5), we need to check if 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5 can be expressed in terms of each other within the field extensions of F 7 F 7 F_(7)\mathbf{F}_7F7.
  1. Square Root of 3 in F 7 F 7 F_(7)\mathbf{F}_7F7: We need to find if there exists an element x F 7 x F 7 x inF_(7)x \in \mathbf{F}_7xF7 such that x 2 3 mod 7 x 2 3 mod 7 x^(2)-=3mod7x^2 \equiv 3 \mod 7x23mod7.
  2. Square Root of 5 in F 7 F 7 F_(7)\mathbf{F}_7F7: Similarly, we need to find if there exists an element y F 7 y F 7 y inF_(7)y \in \mathbf{F}_7yF7 such that y 2 5 mod 7 y 2 5 mod 7 y^(2)-=5mod7y^2 \equiv 5 \mod 7y25mod7.
Let’s perform explicit checks for the existence of 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5 in F 7 F 7 F_(7)\mathbf{F}_7F7:
  • For 3 3 sqrt3\sqrt{3}3: We look for an element x x xxx such that x 2 3 mod 7 x 2 3 mod 7 x^(2)-=3mod7x^2 \equiv 3 \mod 7x23mod7.
  • For 5 5 sqrt5\sqrt{5}5: We look for an element y y yyy such that y 2 5 mod 7 y 2 5 mod 7 y^(2)-=5mod7y^2 \equiv 5 \mod 7y25mod7.
Let’s calculate these explicitly to see if such elements exist and to understand the relationship between F 7 ( 3 ) F 7 ( 3 ) F_(7)(sqrt3)\mathbf{F}_7(\sqrt{3})F7(3) and F 7 ( 5 ) F 7 ( 5 ) F_(7)(sqrt5)\mathbf{F}_7(\sqrt{5})F7(5).
After calculating, we find that there are no integer solutions for x 2 3 mod 7 x 2 3 mod 7 x^(2)-=3mod7x^2 \equiv 3 \mod 7x23mod7 and x 2 5 mod 7 x 2 5 mod 7 x^(2)-=5mod7x^2 \equiv 5 \mod 7x25mod7 within F 7 F 7 F_(7)\mathbf{F}_7F7. This means that neither 3 3 sqrt3\sqrt{3}3 nor 5 5 sqrt5\sqrt{5}5 can be directly represented by any element in F 7 F 7 F_(7)\mathbf{F}_7F7 through simple squaring and modular arithmetic.
However, the statement " F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5)" refers to the equality of field extensions of F 7 F 7 F_(7)\mathbf{F}_7F7 that include 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5, respectively. Given that neither 3 3 sqrt3\sqrt{3}3 nor 5 5 sqrt5\sqrt{5}5 has a direct representation in F 7 F 7 F_(7)\mathbf{F}_7F7, both 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5 would necessitate extensions of F 7 F 7 F_(7)\mathbf{F}_7F7 to be included.
The absence of integer solutions for these equations in F 7 F 7 F_(7)\mathbf{F}_7F7 suggests that both 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5 would lead to the creation of quadratic extensions of F 7 F 7 F_(7)\mathbf{F}_7F7, as both would be roots of irreducible quadratic polynomials over F 7 F 7 F_(7)\mathbf{F}_7F7. The key insight here is not the absence of solutions within F 7 F 7 F_(7)\mathbf{F}_7F7 but the nature of the extensions they generate.
Given the structure of finite fields, any extension of F 7 F 7 F_(7)\mathbf{F}_7F7 to include a square root not in F 7 F 7 F_(7)\mathbf{F}_7F7 would have to be a quadratic extension, implying that both F 7 ( 3 ) F 7 ( 3 ) F_(7)(sqrt3)\mathbf{F}_7(\sqrt{3})F7(3) and F 7 ( 5 ) F 7 ( 5 ) F_(7)(sqrt5)\mathbf{F}_7(\sqrt{5})F7(5) are quadratic extensions of F 7 F 7 F_(7)\mathbf{F}_7F7. Since all quadratic extensions of a given finite field have the same size (in this case, 49 49 494949 elements, or F 7 2 F 7 2 F_(7^(2))\mathbf{F}_{7^2}F72), and since there’s only one field of each possible order in the realm of finite fields, it follows that F 7 ( 3 ) F 7 ( 3 ) F_(7)(sqrt3)\mathbf{F}_7(\sqrt{3})F7(3) and F 7 ( 5 ) F 7 ( 5 ) F_(7)(sqrt5)\mathbf{F}_7(\sqrt{5})F7(5) must indeed be the same field, despite the initial intuition suggested by the absence of direct square roots in F 7 F 7 F_(7)\mathbf{F}_7F7.
Therefore, the statement " F 7 ( 3 ) = F 7 ( 5 ) F 7 ( 3 ) = F 7 ( 5 ) F_(7)(sqrt3)=F_(7)(sqrt5)\mathbf{F}_7(\sqrt{3})=\mathbf{F}_7(\sqrt{5})F7(3)=F7(5)" is true, as both 3 3 sqrt3\sqrt{3}3 and 5 5 sqrt5\sqrt{5}5 lead to the same quadratic extension of F 7 F 7 F_(7)\mathbf{F}_7F7, given the unique structure of finite fields and their extensions.
(e) For any α F 2 5 , α 1 , F 2 5 = F 2 [ α ] α F 2 5 , α 1 , F 2 5 = F 2 [ α ] alpha inF_(2^(5))^(**),alpha!=1,F_(2^(5))=F_(2)[alpha]\alpha \in \mathbb{F}_{2^5}^*, \alpha \neq 1, \mathbb{F}_{2^5}=\mathbb{F}_2[\alpha]αF25,α1,F25=F2[α].
Answer:
The statement "For any α F 2 5 , α 1 , F 2 5 = F 2 [ α ] α F 2 5 , α 1 , F 2 5 = F 2 [ α ] alpha inF_(2^(5))^(**),alpha!=1,F_(2^(5))=F_(2)[alpha]\alpha \in \mathbb{F}_{2^5}^*, \alpha \neq 1, \mathbb{F}_{2^5}=\mathbb{F}_2[\alpha]αF25,α1,F25=F2[α]" concerns the structure of finite fields, specifically the field with 2 5 = 32 2 5 = 32 2^(5)=322^5 = 3225=32 elements, denoted F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25, and the concept of field extensions.
Background:
  • F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 is a finite field with 32 32 323232 elements. It is the splitting field for the polynomial x 32 x x 32 x x^(32)-xx^{32} – xx32x over F 2 F 2 F_(2)\mathbb{F}_2F2, and it contains all roots of this polynomial.
  • F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25 denotes the multiplicative group of F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25, which consists of all non-zero elements of F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25. This group has 31 31 313131 elements, and it is cyclic.
  • F 2 [ α ] F 2 [ α ] F_(2)[alpha]\mathbb{F}_2[\alpha]F2[α] denotes the smallest field containing both F 2 F 2 F_(2)\mathbb{F}_2F2 and the element α α alpha\alphaα. If α α alpha\alphaα is a primitive element of F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 (i.e., a generator of the multiplicative group F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25), then F 2 [ α ] = F 2 5 F 2 [ α ] = F 2 5 F_(2)[alpha]=F_(2^(5))\mathbb{F}_2[\alpha] = \mathbb{F}_{2^5}F2[α]=F25.
  • A primitive element of a finite field is an element whose powers generate all non-zero elements of the field.
Analysis:
The statement asserts that for any non-identity element α α alpha\alphaα of F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25, the field generated by α α alpha\alphaα over F 2 F 2 F_(2)\mathbb{F}_2F2 is the entire field F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25. This would mean that every non-identity element in F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 is a primitive element.
However, this is not true for every non-identity element of F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25. While it is true that a primitive element α α alpha\alphaα (an element of order 31 31 313131) will generate the entire field F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 through its powers, not every non-identity element in F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 is a primitive element. Some elements will have smaller orders due to the structure of the cyclic group F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25. For example, an element of order 3 3 333 would only cycle through 3 3 333 distinct non-zero elements (plus the identity element when raised to the power of 3 3 333) before repeating, and thus, it cannot generate the entire field.
Justification/Proof:
To disprove the statement, we can consider the property of the elements’ orders in F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25. The order of any element α α alpha\alphaα in a finite field must divide the order of the field’s multiplicative group, which is 31 31 313131 in this case (since F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25 has 31 31 313131 elements). By Lagrange’s theorem, the possible orders of elements in F 2 5 F 2 5 F_(2^(5))^(**)\mathbb{F}_{2^5}^*F25 are divisors of 31 31 313131, which are 1 1 111 and 31 31 313131 itself, because 31 31 313131 is a prime number.
Therefore, while an element α α alpha\alphaα with order 31 31 313131 (a primitive element) will indeed generate the entire field F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 through its powers, implying F 2 5 = F 2 [ α ] F 2 5 = F 2 [ α ] F_(2^(5))=F_(2)[alpha]\mathbb{F}_{2^5} = \mathbb{F}_2[\alpha]F25=F2[α] for such α α alpha\alphaα, not every non-identity element has this property, as the statement incorrectly generalizes. Only the primitive elements of F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 can generate the entire field.
Conclusion:
The statement is false because not every non-identity element in F 2 5 F 2 5 F_(2^(5))\mathbb{F}_{2^5}F25 is a primitive element capable of generating the entire field. Only specific elements, namely the primitive elements, have this property.

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