algebra assignment 2
TRANSCRIPT
ALGEBRAIC STRUCTURE ( TMA 3033 )
ASSIGNMENT 2
GROUP A
LECTURER : PUAN NORASHIQIN BT MOHD IDRUS
GROUP MEMBERS :
NAME MATRIC NUMBER
DESIGA A/P VESWANAHAN D20061026152
STEPHANIE KARMINI A/P EMMANUEL GERARD D20061026158
VERONICA SELVI A/P MARATHA MUTHU D20061026163
NAGESWARI A/P YELLAPA APPARAO D20061026166
QUESTION 1
Let Zm and Zn be two groups of integer mod m and n respectively. Define
by ( , ) , with the operation + defined on by
( , ) ( , ) (( ) mod , ( ) mod ) where ( , ) (m n m n m nZ Z a b a Z b Z Z Z
a b c d a c m b d n a b c
, )
we say that is the external direct sum of Zm and Zn.m nd Z Z
QUESTIONS:
(a) Prove that this algebraic structure gives us a group.
(i) closed under operation
Is ? and is [ ]
Since and then, and since and then,
Thus , .
Hence is closed under operation .
( , ) ( , ) m na b c d Z Z ( , ) ( , ) (( ) mod , ( ) mod )a b c d a c m b d n m nZ Z
ma Z mc Z ( ) moda c m nb Z nd Z
( ) modb d n
( , ) ( , ) (( ) mod , ( ) mod ) m na b c d a c m b d n Z Z
m nZ Z
(ii) Associative
( , ) ( , ) ( , ) ( , ) ( , ) ( , )a b c d e f a b c d e f
LHS = ( , ) ( , ) ( , )
= (a+c) mod , (b+d) mod + (e, f)
= ( ) mod , ( ) mod
a b c d e f
m n
a c e m b d f n
RHS = (a, b)+ (c, d)+(e, f)
= ( ) ( ) mod , ( ) mod
= ( ) mod , ( ) mod
a b c e m d f n
a c e m b d f n
LHS=RHS
a, c, e and b, d, f
(a, b)+(c, d)+(e, f)
is associative
m n
m n
m n
Z Z
Z Z
Z Z
(iii) Identity
a b
a b
a b a b
a b
Let e , e are the identities of and respectively.
then e , e is the identity of
Since, (a+b) + e , e = (a+b) = e , e (a+b)
LHS = (a+b) + e , e
m n
m n
Z Z
Z Z
a b
a b
a b
= ( e ) mod , ( e ) mod
= a mod , b mod
RHS = e , e (a+b)
= (e ) mod , (e ) mod
= a mod
a m b n
m n
a m b n
, b modm n
LHS=RHS,
therefore has an identitym nZ Z
(iii) Inverse An inverse of is (a, b) -1 -1(a , b )
-1
-1
m n
-1 -1 -1 -1a b
-1 -1 -1 -1
-1
, a
, b
where Z , Z is group of integer
(a, b) + (a , b ) = e , e (a , b ) + (a, b)
LHS = (a, b) + (a , b ) RHS = (a , b ) + (a, b)
= (a + a
m m
n n
a Z Z
b Z Z
-1 -1 -1
a b a b
)mod , (b + b )mod = (a + a) mod , (b + b) mod
= e mod m, e mod = e mod m, e mod
m n m n
n n
LHS = RHS,
therefore has an inverse
Hence, is a group, which is a external direct sum
m n
m n
Z Z
Z Z
(b)
(a) List all the elements of
(b) Show whether cyclic is cyclic or not?
2 2Z Z
2
2 2
0,1
( , ) ,
(0,0), (0,1), (1,0), (1,1)
m n m n
Z
Z Z a b a Z b Z
Z Z
2 2Z Z
2 2
2 2 2
(0,0), (0,1), (1,0), (1,1)
0,0 (0 ,0 ) m, n (0,0)
0,1 (0 ,1 ) m, n (0,0), (0,1)
1,0 (1 ,0 ) m, n (0,0), (1,0)
1,1 (1 ,1 ) m, n (0,0), (1,1)
is not a cyclic group as no element of
m n
m n
m n
m n
Z Z
Z
Z
Z
Z
Z Z Z Z
2 2 2 generate Z Z
Does not generate
2 2Z Z
(c)
gcd(2, 2) = 2 non-cyclic gcd(3, 4) = 1 cyclic
gcd(2, 3) = 1 cyclic gcd(3, 5) = 1 cyclic
gcd(2, 4) =2 non-cyclic gcd(2, 5) = 1 cyclic
gcd(3,6) = 3 non-cyclic gcd(3,7) =1 cyclic
gcd(3,8) = 1 cyclic gcd(3, 9) = 3 non-cyclic
gcd(4, 6) = 2 non-cyclic
We can check the other basis gcd and find that for the basis with the gcd 1 it is cyclic.The basis will only be cyclic if the gcd (m,n) = 1
(m,n) Character (m,n) Character
(2,2) Non cyclic (3,6) Non cyclic
(2,3) Cyclic (3,7) Cyclic
(2,4) Non cyclic (3,8) Cyclic
(2,5) Cyclic (3,9) Non cyclic
(3,4) Cyclic (4,6) Non cyclic
(3,5) Cyclic
(0,0) (0,1) (1,0) (1,1)
(0,0) (0,0) (0,1) (1,0) (1,1)
(0,1) (0,1) (0,0) (1,1) (1,0)
(1,0) (1,0) (1,1) (0,0) (0,1)
(1,1) (1,1) (1,0) (0,1) (0,0)
(e,e) (e,a) (a,e) (a,a)
(e,e) (e,e) (e,a) (a,e) (a,a)
(e,a) (e,a) (e,e) (a,a) (a,e)
(a,e) (a,e) (a,a) (e,e) (e,a)
(a,a) (a,a) (a,e) (e,a) (e,e)
2 2Z Z 2 2V V
and are different but isomorphic The one to one correspondence
(0,0) can substitute by (e,e) (0,0) (e,e)
(0,1) can substitute by (e,
G G
a) (0,1) (e,a)
(1,0) can substitute by (a,e) (1,0) (a,e)
(1,1) can substitute by (a,a) (1,1) (a,a
)
transforms to and ; and are isomorphic to each other because there exist an isomorphism
from the Cayley Table to the Klein Group.
G G G G
(d) By using Cayley Table, show that is isomorphic to the Klein four group, V2 2Z Z
2 2 2 2
2 2 2 2
:
: where G = and
Z Z V V
G G Z Z G V V
(c)(a)
3 2
3 2
3 2
(3,2)
0,1,2 0,1
(0,0), (0,1), (1,0), (1,1), (2,0), (2,1)
Z Z
Z Z
Z Z
4 4
4
4 4
(4,4)
0,1,2,3
{(0,0), (0,1), (0,2), (0,3), (1,0), (1,1), (1, 2), (1,3), (2,0), (2,1), (2,2),
(2,3),(3,0),(3,1),(3,2),(3,3)}
Z Z
Z
Z Z
3 4
3 4
3 4
(3,4)
0,1,2 0,1,2,3
{(0,0), (0,1), (0,2), (0,3), (1,0), (1,1), (1, 2), (1,3), (2,0), (2,1), (2,2), (2,3)}
Z Z
Z Z
Z Z
6 2
4 2
6 2
(6,2)
0,1,2,3,4,5 0,1
{(0,0), (0,1), (1,0), (1,1), (2,0), (2,1),(3,0),(3,1),(4,0)(4,1),(5,0)(5,1)}
Z Z
Z Z
Z Z
(b)3 2
4 4
3 4
6 2
order of (3,2) = 6 = (3 2)
order of (4,4) = 16 =(4 4)
order of (3,4) = 12 =(3 4)
order of (6,2) = 12 =(6 2)
From this we can make the conjecture that the or
Z Z
Z Z
Z Z
Z Z
der of
The Proof :
= (m) (n)
= mn
m n
m n m n
Z Z mn
Z Z Z Z
QUESTION 2
The group of quaternions denoted by Q4 consists of the following elements ,
is defined by the following Cayley’s table :
2 3 2 3, , , , , , ,e a a a b ba ba baQ4
eee
ee
ee
ee
e
a
aa
aa
aa
a
a
a
2a
2a
2a
2a
2a
2a2a
2a
2a
2a
3a
3a
3a
3a
3a
3a3a
3a3a
3a
b
bb
bb
b
b
bb
b
baba
ba
baba
baba
baba
ba
2ba2ba
2ba2ba
2ba
2ba
2ba
2ba2ba
2ba3ba 3ba
3ba3ba
3ba
3ba3ba
3ba
3ba3ba
Q4
Questions :
Use the table to determine each of the following (Show your answer) :
a) The center of Q4.
b) All cyclic subgroups of Q4.
c) cl(a) & cl(b) where cl(a) is defined as below :
let G be a group. For each , defined the conjugacy class of a, cl (a) as
a G
1( )cl a xax x G
4a THE CENTER OF Q
4 4
4
The center of is a commutative subgroup of ,
denoted by
and define by :
Q Q
Z(Q )
4 4 4:Z(Q ) = a Q aq = qa, q Q
Therefore,
From the Cayley 's table :
This is because
2
2 3 2
3 3
3
ae = a = ea
aa = a = aa
aa = a = a a
aa = e = a a
ab = ba ba ba = ba
:a
2 2 2
2 3 2
2 2 2 2
2 3 3 2
2 2 2
2 3 2
2 2 2 2
2 3 3 2
a e = a = ea
a a = a = aa
a a = e = a a
a a = a = a a
a b = ba = ba
a ba = ba = ba a
a ba = b = ba a
a ba = ba = ba a
:2a
This is because
3 3 3
3 3
3 2 2 3
3 3 2 3 3
3 3 3 3
a e = a = ea
a a = e = aa
a a = a = a a
a a = a = a a
a b = ba ba ba = ba
:3a
This is because 3
be = b = eb
ba = ba ab ab = ba
:b
This is because2
ba e = ba = e ba
ba a = ba a ba a ba = b
:ba
This is because
2 2 2
2 3 2 2
ba e = ba = e ba
ba a = ba a ba a ba = ba
:2ba
This is because
3 3 3
3 3 3 2
ba e = ba = e ba
ba a = b a ba a ba = ba
:3ba
4
4
From the Cayley 's table, it is shown that is the
commutative subgroup of which means
and identity is the center of .
2
2
a
Q
a e Q
4Therefore, 2Z Q e,a
4
b
ALL CYCLIC
SUBGROUP OF Q
4 4, nFor any q Q the subgroup H x Q x q for n Z
4.is called thecyclic subgroup of Q
, :Thus fromthetable
1
2 3 2 32 4
2 2 23
3 3 3 24 2
2 25
2 36
2 2 2 27
3 3 3 28
1, , , , , , , sin 1
( ) ,
( ) , , ,
, , ,
( ) , , ,
( ) , , ,
( ) , , ,
n
n
n
n
n
n
n
n
H e e n Z e
H a a n Z a a a e a a a e ce Q
H a a n Z a e
H a a n Z a a a e H
H b b n Z b a ba e
H ba ba n Z ba a ba e
H ba ba n Z ba a b e
H ba ba n Z ba a ba 6e H
c
cl(a) & cl(b)
14i ( ) cl a qaq q Q
1
1 3
2 2 1 2 2
3 3 1 3
1 2 3
1 3 3
2 2 2 3
3 3 1 3 3
1)
2)
3) ( )
4) ( )
5) ( ) ( )
6) ( ) ( ) ( ) ( )
7)( ) ( ) ( ) ( )
8) ( ) ( ) ( ) ( )
eae a
aaa aaa a
a a a a aa a
a a a a aa a
bab b a ba a
ba a ba ba a ba a
ba a ba ba a b a
ba a ba ba a ba a
1
1 3 2
2 2 1 2 2
3 3 1 3 2
1 2
1 3 2
2 2 2
3 3 1 3 2
1)
2)
3) ( )
4) ( )
5) ( ) ( )
6) ( ) ( ) ( ) ( )
7) ( ) ( ) ( ) ( )
8) ( ) ( ) ( ) ( )
ebe b
aba aba ba
a b a a ba b
a b a a ba ba
bbb b b ba b
ba b ba ba b ba ba
ba b ba ba b b b
ba b ba ba b ba ba
14ii ( ) cl b qbq q Q
THE END