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 Page 1


Edurev123 
3. Fields 
3.1 Consider the polynomial ring ?? [?? ]. Show ?? (?? )=?? ?? -?? is irreducible over ?? . 
Let ?? be the ideal in ?? [?? ] generated by ?? (?? ) . Then show that ?? [?? ]/?? is a field and 
that each element is of the form ?? ?? +?? ?? ?? +?? ?? ?? ?? with ?? ,?? ?? ,?? ?? in ?? and ?? =?? +?? . 
(2010 : 15 Marks) 
Solution: 
Given : 
?? (?? )=?? 3
-2 
Let ?? (?? ),?? (?? )??? [?? ], and ?? (?? ) is reducible such that 
?? (?? ) =?? (?? )·?? (?? )
 Suppose, ?? (?? ) =?? +?? ? ?? (?? ) =?? 2
+?? ?? +?? ???? (?? ) =?? 3
-2=(?? +?? )(?? 2
+???? +?? )
? ?? 3
-2 =?? 3
+?? ?? 2
+???? +?? ?? 2
+???? +????
 
Comparing LHS & RHS, we get 
?? +?? ?=0??? =-?? ???? +?? ?=0
??-?? 2
+?? ?=0??? =?? 2
???? ?=-2
???? 3
?=-2??? =-2
1/3
 which is not a rational number 
 
i.e., ?? ??? ??? ,?? ??? 
??? (?? ) is irreducible over ?? . 
Now, ?? is ideal generated by ?? (?? ) 
i.e., 
?? =??? (?? )? 
?
?? (?? )
?? is a field as ?? (?? ) is irreducible (theorem) 
Page 2


Edurev123 
3. Fields 
3.1 Consider the polynomial ring ?? [?? ]. Show ?? (?? )=?? ?? -?? is irreducible over ?? . 
Let ?? be the ideal in ?? [?? ] generated by ?? (?? ) . Then show that ?? [?? ]/?? is a field and 
that each element is of the form ?? ?? +?? ?? ?? +?? ?? ?? ?? with ?? ,?? ?? ,?? ?? in ?? and ?? =?? +?? . 
(2010 : 15 Marks) 
Solution: 
Given : 
?? (?? )=?? 3
-2 
Let ?? (?? ),?? (?? )??? [?? ], and ?? (?? ) is reducible such that 
?? (?? ) =?? (?? )·?? (?? )
 Suppose, ?? (?? ) =?? +?? ? ?? (?? ) =?? 2
+?? ?? +?? ???? (?? ) =?? 3
-2=(?? +?? )(?? 2
+???? +?? )
? ?? 3
-2 =?? 3
+?? ?? 2
+???? +?? ?? 2
+???? +????
 
Comparing LHS & RHS, we get 
?? +?? ?=0??? =-?? ???? +?? ?=0
??-?? 2
+?? ?=0??? =?? 2
???? ?=-2
???? 3
?=-2??? =-2
1/3
 which is not a rational number 
 
i.e., ?? ??? ??? ,?? ??? 
??? (?? ) is irreducible over ?? . 
Now, ?? is ideal generated by ?? (?? ) 
i.e., 
?? =??? (?? )? 
?
?? (?? )
?? is a field as ?? (?? ) is irreducible (theorem) 
???
?? (?? )
?? =??? (?? )>+?? 0
+?? 1
?? +?? 2
?? 2
=?? +?? 0
+?? 1
?? +?? 2
?? 2
deg·(?? 0
+?? 1
?? +?? 2
?? 2
)<deg·(?? (?? ))
?????????????????????
 remainder term 
 
where ?? 0
,?? 1
,?? 2
??? . Now, 
?? ?=?? +?? ?? 0
+?? 1
?? +?? 2
?? 2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )
2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )(?? +?? )
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? 2
+?? )
?=?? 0
+?? 1
?? +?? 2
?? 2
+?? which is equivalent to eqn. (1) 
 
?
?? (?? )
?? can be written as ?? 0
+?? 1
?? +?? 2
2
2
 where ?? =?? +?? . 
3.2 Show that the set of matrices ?? ={[
?? -?? ?? ?? ]?? ,?? ??? } is a field under the usual 
binary operations of matrix addition and matrix multiplication. What are the 
additive and multiplicative identities and what is the inverse of [
?? -?? ?? ?? ] ? Consider 
iiie map ?? :?? ??? defined by ?? (?? +???? )=[
?? -?? ?? ?? ]. Show that ?? is an isomorphism 
(Here ?? is the set of real numbers and ?? is the set of complex numbers)? 
(2013 : 10 Marks) 
Solution: 
Approach : Prove only the important parts in actual exam. 
SCM?(2,?? ) where ?? (?? ,?? ) is the ring of 2×2 matrices with entries from ?? . 
To show ?? is a field 
and 
[
?? -?? ?? ?? ]??? ?[
?? -?? ?? ?? ]
-1
=[
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]
-1
??? [
?? -?? ?? ?? ][
?? -?? ?? ?? ]
-1
=[
?? -?? ?? ?? ][
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]=[
???? +????
?? 2
+?? 2
-(???? -???? )
?? 2
+?? 2
???? -????
?? 2
+?? 2
???? +????
?? 2
+?? 2
]??? 
So, ?? is closed w.r.t. multiplication and has multiplicative inverse. 
Also, 
Page 3


Edurev123 
3. Fields 
3.1 Consider the polynomial ring ?? [?? ]. Show ?? (?? )=?? ?? -?? is irreducible over ?? . 
Let ?? be the ideal in ?? [?? ] generated by ?? (?? ) . Then show that ?? [?? ]/?? is a field and 
that each element is of the form ?? ?? +?? ?? ?? +?? ?? ?? ?? with ?? ,?? ?? ,?? ?? in ?? and ?? =?? +?? . 
(2010 : 15 Marks) 
Solution: 
Given : 
?? (?? )=?? 3
-2 
Let ?? (?? ),?? (?? )??? [?? ], and ?? (?? ) is reducible such that 
?? (?? ) =?? (?? )·?? (?? )
 Suppose, ?? (?? ) =?? +?? ? ?? (?? ) =?? 2
+?? ?? +?? ???? (?? ) =?? 3
-2=(?? +?? )(?? 2
+???? +?? )
? ?? 3
-2 =?? 3
+?? ?? 2
+???? +?? ?? 2
+???? +????
 
Comparing LHS & RHS, we get 
?? +?? ?=0??? =-?? ???? +?? ?=0
??-?? 2
+?? ?=0??? =?? 2
???? ?=-2
???? 3
?=-2??? =-2
1/3
 which is not a rational number 
 
i.e., ?? ??? ??? ,?? ??? 
??? (?? ) is irreducible over ?? . 
Now, ?? is ideal generated by ?? (?? ) 
i.e., 
?? =??? (?? )? 
?
?? (?? )
?? is a field as ?? (?? ) is irreducible (theorem) 
???
?? (?? )
?? =??? (?? )>+?? 0
+?? 1
?? +?? 2
?? 2
=?? +?? 0
+?? 1
?? +?? 2
?? 2
deg·(?? 0
+?? 1
?? +?? 2
?? 2
)<deg·(?? (?? ))
?????????????????????
 remainder term 
 
where ?? 0
,?? 1
,?? 2
??? . Now, 
?? ?=?? +?? ?? 0
+?? 1
?? +?? 2
?? 2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )
2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )(?? +?? )
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? 2
+?? )
?=?? 0
+?? 1
?? +?? 2
?? 2
+?? which is equivalent to eqn. (1) 
 
?
?? (?? )
?? can be written as ?? 0
+?? 1
?? +?? 2
2
2
 where ?? =?? +?? . 
3.2 Show that the set of matrices ?? ={[
?? -?? ?? ?? ]?? ,?? ??? } is a field under the usual 
binary operations of matrix addition and matrix multiplication. What are the 
additive and multiplicative identities and what is the inverse of [
?? -?? ?? ?? ] ? Consider 
iiie map ?? :?? ??? defined by ?? (?? +???? )=[
?? -?? ?? ?? ]. Show that ?? is an isomorphism 
(Here ?? is the set of real numbers and ?? is the set of complex numbers)? 
(2013 : 10 Marks) 
Solution: 
Approach : Prove only the important parts in actual exam. 
SCM?(2,?? ) where ?? (?? ,?? ) is the ring of 2×2 matrices with entries from ?? . 
To show ?? is a field 
and 
[
?? -?? ?? ?? ]??? ?[
?? -?? ?? ?? ]
-1
=[
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]
-1
??? [
?? -?? ?? ?? ][
?? -?? ?? ?? ]
-1
=[
?? -?? ?? ?? ][
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]=[
???? +????
?? 2
+?? 2
-(???? -???? )
?? 2
+?? 2
???? -????
?? 2
+?? 2
???? +????
?? 2
+?? 2
]??? 
So, ?? is closed w.r.t. multiplication and has multiplicative inverse. 
Also, 
[
?? -?? ?? ?? ][
?? -?? ?? ?? ]=[
???? -???? -(???? +???? )
???? +???? ???? -????
]=[
?? -?? ?? ?? ][
?? -?? ?? ?? ] 
i.e., multiplication is commutative. 
That addition is commutative, closed and has inverse follows from ?? being subset of 
?? (2,?? ) . ??? is a field. 
Additive identity : 
[
?? -?? ?? ?? ]+[
0 0
0 0
]=[
?? -?? ?? ?? ]=[
0 0
0 0
]+[
?? -?? ?? ?? ] 
?[
0 0
0 0
]??? is additive identity. 
Similarly, [
1 0
0 1
]=?? 2
 is multiplicative identity. 
[
1 -1
1 1
]
-1
=[
1
2
1
2
-1
2
1
2
]??? ?? (?? +???? )=[
?? -?? ?? ?? ]
 
To show ?? is isomorphism, ?? is linear. 
?? (?? +???? )+(?? +???? )]?=?? (?? +?? +??(?? +?? )]
?=[
?? +?? -(?? +?? )
?? +?? ?? +?? ]=[
?? -?? ?? ?? ]+[
?? -?? ?? ?? ]
 
3.3 Show that ?? ?? is a field. Then find ([?? ]+[?? ])
-?? and (-[?? ])
-?? in ?? ?? . 
(2014 : 15 Marks) 
Solution: 
?? 7
={[0],[1],[2],[3],[4],[5],[6]} 
For ?? 7
 to be a field, it should satisfy 
 (i) (?? 7
,+) is an abelian. 
(ii) (?? 7
,?? ) is an abelian group, where ?? 7
*
=?? 7
-{0} 
(iii) Distributive law. 
(i) (?? 7
+) 
+ [0] [1] [2] [3] [4] [5] [6] 
Page 4


Edurev123 
3. Fields 
3.1 Consider the polynomial ring ?? [?? ]. Show ?? (?? )=?? ?? -?? is irreducible over ?? . 
Let ?? be the ideal in ?? [?? ] generated by ?? (?? ) . Then show that ?? [?? ]/?? is a field and 
that each element is of the form ?? ?? +?? ?? ?? +?? ?? ?? ?? with ?? ,?? ?? ,?? ?? in ?? and ?? =?? +?? . 
(2010 : 15 Marks) 
Solution: 
Given : 
?? (?? )=?? 3
-2 
Let ?? (?? ),?? (?? )??? [?? ], and ?? (?? ) is reducible such that 
?? (?? ) =?? (?? )·?? (?? )
 Suppose, ?? (?? ) =?? +?? ? ?? (?? ) =?? 2
+?? ?? +?? ???? (?? ) =?? 3
-2=(?? +?? )(?? 2
+???? +?? )
? ?? 3
-2 =?? 3
+?? ?? 2
+???? +?? ?? 2
+???? +????
 
Comparing LHS & RHS, we get 
?? +?? ?=0??? =-?? ???? +?? ?=0
??-?? 2
+?? ?=0??? =?? 2
???? ?=-2
???? 3
?=-2??? =-2
1/3
 which is not a rational number 
 
i.e., ?? ??? ??? ,?? ??? 
??? (?? ) is irreducible over ?? . 
Now, ?? is ideal generated by ?? (?? ) 
i.e., 
?? =??? (?? )? 
?
?? (?? )
?? is a field as ?? (?? ) is irreducible (theorem) 
???
?? (?? )
?? =??? (?? )>+?? 0
+?? 1
?? +?? 2
?? 2
=?? +?? 0
+?? 1
?? +?? 2
?? 2
deg·(?? 0
+?? 1
?? +?? 2
?? 2
)<deg·(?? (?? ))
?????????????????????
 remainder term 
 
where ?? 0
,?? 1
,?? 2
??? . Now, 
?? ?=?? +?? ?? 0
+?? 1
?? +?? 2
?? 2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )
2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )(?? +?? )
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? 2
+?? )
?=?? 0
+?? 1
?? +?? 2
?? 2
+?? which is equivalent to eqn. (1) 
 
?
?? (?? )
?? can be written as ?? 0
+?? 1
?? +?? 2
2
2
 where ?? =?? +?? . 
3.2 Show that the set of matrices ?? ={[
?? -?? ?? ?? ]?? ,?? ??? } is a field under the usual 
binary operations of matrix addition and matrix multiplication. What are the 
additive and multiplicative identities and what is the inverse of [
?? -?? ?? ?? ] ? Consider 
iiie map ?? :?? ??? defined by ?? (?? +???? )=[
?? -?? ?? ?? ]. Show that ?? is an isomorphism 
(Here ?? is the set of real numbers and ?? is the set of complex numbers)? 
(2013 : 10 Marks) 
Solution: 
Approach : Prove only the important parts in actual exam. 
SCM?(2,?? ) where ?? (?? ,?? ) is the ring of 2×2 matrices with entries from ?? . 
To show ?? is a field 
and 
[
?? -?? ?? ?? ]??? ?[
?? -?? ?? ?? ]
-1
=[
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]
-1
??? [
?? -?? ?? ?? ][
?? -?? ?? ?? ]
-1
=[
?? -?? ?? ?? ][
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]=[
???? +????
?? 2
+?? 2
-(???? -???? )
?? 2
+?? 2
???? -????
?? 2
+?? 2
???? +????
?? 2
+?? 2
]??? 
So, ?? is closed w.r.t. multiplication and has multiplicative inverse. 
Also, 
[
?? -?? ?? ?? ][
?? -?? ?? ?? ]=[
???? -???? -(???? +???? )
???? +???? ???? -????
]=[
?? -?? ?? ?? ][
?? -?? ?? ?? ] 
i.e., multiplication is commutative. 
That addition is commutative, closed and has inverse follows from ?? being subset of 
?? (2,?? ) . ??? is a field. 
Additive identity : 
[
?? -?? ?? ?? ]+[
0 0
0 0
]=[
?? -?? ?? ?? ]=[
0 0
0 0
]+[
?? -?? ?? ?? ] 
?[
0 0
0 0
]??? is additive identity. 
Similarly, [
1 0
0 1
]=?? 2
 is multiplicative identity. 
[
1 -1
1 1
]
-1
=[
1
2
1
2
-1
2
1
2
]??? ?? (?? +???? )=[
?? -?? ?? ?? ]
 
To show ?? is isomorphism, ?? is linear. 
?? (?? +???? )+(?? +???? )]?=?? (?? +?? +??(?? +?? )]
?=[
?? +?? -(?? +?? )
?? +?? ?? +?? ]=[
?? -?? ?? ?? ]+[
?? -?? ?? ?? ]
 
3.3 Show that ?? ?? is a field. Then find ([?? ]+[?? ])
-?? and (-[?? ])
-?? in ?? ?? . 
(2014 : 15 Marks) 
Solution: 
?? 7
={[0],[1],[2],[3],[4],[5],[6]} 
For ?? 7
 to be a field, it should satisfy 
 (i) (?? 7
,+) is an abelian. 
(ii) (?? 7
,?? ) is an abelian group, where ?? 7
*
=?? 7
-{0} 
(iii) Distributive law. 
(i) (?? 7
+) 
+ [0] [1] [2] [3] [4] [5] [6] 
[0] [0] [1] [2] [3] [4] [5] [6] 
[1] [1] [2] [3] [4] [5] [6] [0] 
[2] [2] [3] [4] [5] [6] [0] [1] 
[3] [3] [4] [5] [6] [0] [1] [2] 
[4] [4] [5] [6] [0] [1] [2] [3] 
[5] [5] [6] [0] [1] [2] [3] [4] 
[6] [6] [0] [1] [2] [3] [4] [5] 
 
? All elements belong to ?? 7
 - closure property. 
? First row coincide with the top row, then [0] is identity element. 
? [0] is in every row & column 
? Inverse property satisfied. 
([?? ]+[?? ]+[?? ]=[?? +?? ]+[?? ]=[?? +?? +?? ]=[?? ]+[?? +?? ]=[?? ]+([?? ]+[?? ]) 
? Associative property satisfied. 
? Transpose of matrix equal to original matrix. 
? Commutative property satisfy. 
(ii) (?? 7
*
,?? ) 
 
? Every element belong to ?? 7
*
-closure property. 
? Top row coincide with first row, Hence [1] is an identity element. 
Page 5


Edurev123 
3. Fields 
3.1 Consider the polynomial ring ?? [?? ]. Show ?? (?? )=?? ?? -?? is irreducible over ?? . 
Let ?? be the ideal in ?? [?? ] generated by ?? (?? ) . Then show that ?? [?? ]/?? is a field and 
that each element is of the form ?? ?? +?? ?? ?? +?? ?? ?? ?? with ?? ,?? ?? ,?? ?? in ?? and ?? =?? +?? . 
(2010 : 15 Marks) 
Solution: 
Given : 
?? (?? )=?? 3
-2 
Let ?? (?? ),?? (?? )??? [?? ], and ?? (?? ) is reducible such that 
?? (?? ) =?? (?? )·?? (?? )
 Suppose, ?? (?? ) =?? +?? ? ?? (?? ) =?? 2
+?? ?? +?? ???? (?? ) =?? 3
-2=(?? +?? )(?? 2
+???? +?? )
? ?? 3
-2 =?? 3
+?? ?? 2
+???? +?? ?? 2
+???? +????
 
Comparing LHS & RHS, we get 
?? +?? ?=0??? =-?? ???? +?? ?=0
??-?? 2
+?? ?=0??? =?? 2
???? ?=-2
???? 3
?=-2??? =-2
1/3
 which is not a rational number 
 
i.e., ?? ??? ??? ,?? ??? 
??? (?? ) is irreducible over ?? . 
Now, ?? is ideal generated by ?? (?? ) 
i.e., 
?? =??? (?? )? 
?
?? (?? )
?? is a field as ?? (?? ) is irreducible (theorem) 
???
?? (?? )
?? =??? (?? )>+?? 0
+?? 1
?? +?? 2
?? 2
=?? +?? 0
+?? 1
?? +?? 2
?? 2
deg·(?? 0
+?? 1
?? +?? 2
?? 2
)<deg·(?? (?? ))
?????????????????????
 remainder term 
 
where ?? 0
,?? 1
,?? 2
??? . Now, 
?? ?=?? +?? ?? 0
+?? 1
?? +?? 2
?? 2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )
2
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? +?? )(?? +?? )
?=?? 0
+?? 1
(?? +?? )+?? 2
(?? 2
+?? )
?=?? 0
+?? 1
?? +?? 2
?? 2
+?? which is equivalent to eqn. (1) 
 
?
?? (?? )
?? can be written as ?? 0
+?? 1
?? +?? 2
2
2
 where ?? =?? +?? . 
3.2 Show that the set of matrices ?? ={[
?? -?? ?? ?? ]?? ,?? ??? } is a field under the usual 
binary operations of matrix addition and matrix multiplication. What are the 
additive and multiplicative identities and what is the inverse of [
?? -?? ?? ?? ] ? Consider 
iiie map ?? :?? ??? defined by ?? (?? +???? )=[
?? -?? ?? ?? ]. Show that ?? is an isomorphism 
(Here ?? is the set of real numbers and ?? is the set of complex numbers)? 
(2013 : 10 Marks) 
Solution: 
Approach : Prove only the important parts in actual exam. 
SCM?(2,?? ) where ?? (?? ,?? ) is the ring of 2×2 matrices with entries from ?? . 
To show ?? is a field 
and 
[
?? -?? ?? ?? ]??? ?[
?? -?? ?? ?? ]
-1
=[
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]
-1
??? [
?? -?? ?? ?? ][
?? -?? ?? ?? ]
-1
=[
?? -?? ?? ?? ][
?? ?? 2
+?? 2
?? ?? 2
+?? 2
-?? ?? 2
+?? 2
?? ?? 2
+?? 2
]=[
???? +????
?? 2
+?? 2
-(???? -???? )
?? 2
+?? 2
???? -????
?? 2
+?? 2
???? +????
?? 2
+?? 2
]??? 
So, ?? is closed w.r.t. multiplication and has multiplicative inverse. 
Also, 
[
?? -?? ?? ?? ][
?? -?? ?? ?? ]=[
???? -???? -(???? +???? )
???? +???? ???? -????
]=[
?? -?? ?? ?? ][
?? -?? ?? ?? ] 
i.e., multiplication is commutative. 
That addition is commutative, closed and has inverse follows from ?? being subset of 
?? (2,?? ) . ??? is a field. 
Additive identity : 
[
?? -?? ?? ?? ]+[
0 0
0 0
]=[
?? -?? ?? ?? ]=[
0 0
0 0
]+[
?? -?? ?? ?? ] 
?[
0 0
0 0
]??? is additive identity. 
Similarly, [
1 0
0 1
]=?? 2
 is multiplicative identity. 
[
1 -1
1 1
]
-1
=[
1
2
1
2
-1
2
1
2
]??? ?? (?? +???? )=[
?? -?? ?? ?? ]
 
To show ?? is isomorphism, ?? is linear. 
?? (?? +???? )+(?? +???? )]?=?? (?? +?? +??(?? +?? )]
?=[
?? +?? -(?? +?? )
?? +?? ?? +?? ]=[
?? -?? ?? ?? ]+[
?? -?? ?? ?? ]
 
3.3 Show that ?? ?? is a field. Then find ([?? ]+[?? ])
-?? and (-[?? ])
-?? in ?? ?? . 
(2014 : 15 Marks) 
Solution: 
?? 7
={[0],[1],[2],[3],[4],[5],[6]} 
For ?? 7
 to be a field, it should satisfy 
 (i) (?? 7
,+) is an abelian. 
(ii) (?? 7
,?? ) is an abelian group, where ?? 7
*
=?? 7
-{0} 
(iii) Distributive law. 
(i) (?? 7
+) 
+ [0] [1] [2] [3] [4] [5] [6] 
[0] [0] [1] [2] [3] [4] [5] [6] 
[1] [1] [2] [3] [4] [5] [6] [0] 
[2] [2] [3] [4] [5] [6] [0] [1] 
[3] [3] [4] [5] [6] [0] [1] [2] 
[4] [4] [5] [6] [0] [1] [2] [3] 
[5] [5] [6] [0] [1] [2] [3] [4] 
[6] [6] [0] [1] [2] [3] [4] [5] 
 
? All elements belong to ?? 7
 - closure property. 
? First row coincide with the top row, then [0] is identity element. 
? [0] is in every row & column 
? Inverse property satisfied. 
([?? ]+[?? ]+[?? ]=[?? +?? ]+[?? ]=[?? +?? +?? ]=[?? ]+[?? +?? ]=[?? ]+([?? ]+[?? ]) 
? Associative property satisfied. 
? Transpose of matrix equal to original matrix. 
? Commutative property satisfy. 
(ii) (?? 7
*
,?? ) 
 
? Every element belong to ?? 7
*
-closure property. 
? Top row coincide with first row, Hence [1] is an identity element. 
? [1] is in every row & column. 
? inverse property satisfied. 
? ([?? ]×[?? ]×[?? ]=[(?? ×?? )×[?? ]=[?? ×?? ×?? ]=[?? ]×[?? ×?? ]=[?? ]×([?? ]×[?? ]) . 
? Associative property satisfied. 
? Transpose of matrix is equal to original matrix. 
? Commutative property satisfy. 
(iii) Distributivity : 
[?? ]×([?? ]×[?? ])?=[?? ]×([?? +?? ])=[?? (?? +?? )]
?=[???? +???? ]=[???? ]+[???? ]=[?? ][?? ]+[?? ][?? ]
([?? ]+[?? ])×[?? ]?=[?? ][?? ]+[?? ][?? ]
 
Similarly 
??????????????????????????????????([5]+[6])
-1
???????? ?=[4]
-1
=[2]
???????????????????????????????????(-[4])
-1
?????????=([3])
-1
=[5]
 
3.4 Show that the set {?? +???? :?? ?? =?? } , where ?? and ?? are real numbers, is a field 
with respect to usual addition and multiplication. 
(2014 : 15 Marks) 
Solution: 
Let ?????????????????????????????????????? ={(?? +???? );?? 3
=1;?? ,?? ?|?? } 
(i) Let (?? ,+) be an algebraic structure. 
?(?? +???? ),(?? +???? )??? . 
(?? +???? )+(?? +???? )?=(?? +?? )+(?? +?? )?? ?=?? +???? -(?? +?? )?|?? 
? Closure property satisfy. 
(ii) Let, (?? +???? ),(?? +???? ),(?? +???? )??? . 
[(?? +???? )+(?? +???? )]?=((?? +?? )+(?? +?? )?? )+(?? +???? ) 
????????????????????????????????????????????????????????????????????????????=(?? +?? +?? )+(?? +?? +?? )w???????????????????????????(i) 
(?? +?? +?? )?R 
(?? +?? +?? )?|?? 
?? +???? )+[(?? +???? )+(?? +???? )]=(?? +???? )+[(?? +?? )+(?? +?? )?? ] 
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FAQs on Fields - Mathematics Optional Notes for UPSC

1. What is the eligibility criteria for the UPSC exam?
Ans. To be eligible for the UPSC exam, candidates must be a citizen of India, have a bachelor's degree from a recognized university, and be between the ages of 21 and 32 years (relaxation in age limit for certain categories).
2. How many attempts are allowed for the UPSC exam?
Ans. General category candidates can attempt the UPSC exam a maximum of 6 times, while OBC category candidates can attempt it 9 times. There is no limit on the number of attempts for SC/ST category candidates.
3. What is the exam pattern for the UPSC exam?
Ans. The UPSC exam consists of three stages - Preliminary examination (objective type), Main examination (descriptive type), and Personality Test (Interview). The Preliminary exam has two papers - General Studies and CSAT (Civil Services Aptitude Test).
4. How can I prepare for the UPSC exam effectively?
Ans. To prepare for the UPSC exam effectively, candidates should create a study schedule, focus on current affairs, practice previous year question papers, and revise regularly. It is also important to stay updated with the syllabus and exam pattern.
5. What are the optional subjects available for the UPSC exam?
Ans. The UPSC exam offers a wide range of optional subjects for the Main examination, including History, Geography, Public Administration, Sociology, Political Science, and Economics, among others. Candidates can choose one optional subject based on their interest and background.
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