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Elementary Group Theory - Exercise 3.4 : Class 12 Math

Complete Exercise 3.4 Elementary Group Theory. Exercise 3.4: Elementary Properties of Group Complete Que Ans note, Class 12 Mathematics.
Elementary Group Theory - Exercise 3.4 : Class 12 Math

Chapter 1: Elementary Group Theory.

Exercise: 3.4


Complete Exercise of Elementary Group Theory - Exercise 3.3 : Class 12 Mathematics 2080 NEB.

Exercise 3.4 is about: Elementary Proerties of Group

Read: NEB Class 12 Mathematics All Chapter Exercise

1. If a and b are the elements of a group (G, *) such that

a) a * b = b, prove that a = e


a * b = b

or, (a * b) * b-1 = b * b-1

or, a * (b * b-1) = b * b-1

or, a * e = e

or, a = e


b.a * b = e, prove that b = a^-1.


a * b = e

or, a-1 * (a * b) = a-1 * e

or, (a-1 * a) * b = a-1 * e

or, e * b = a-1.

or, b = a-1.


2. If the group ( G, ㅇ) is commutative show that (a ㅇ b)^-1 = a^-1 ㅇ b^-1, for all a, b ∊ G.


(a o b) o (a-1 o b-1) = ((a o b) o a-1) o b-1    [by associative law]

= ((b o a) o a-1) o b-1    [by commutative law]

= (b o (a o a-1)) o b-1   [by associative law]

= (b o e) o b-1   [a o a-1 = e, identity element of G]

= b o b-1    [b o e = b]

= e.

Similarly, (a-1 o b-1) o (a o b) = e.

So, a-1 o b-1 is the inverse of a o b.

i.e. (a o b)-1 = a-1 o b-1.


3. Prove that if every element of a group G is its own inverse, then G is abelian.


Given G is a group such that a = a-1 for all a ԑ G. To prove G is abelian, let a,b ԑ G, then a * b ԑ G, where * is the binary operation of G.

Now, (a * b) = (a * b)-1.

= b-1 * a-1 = b * a.

Thus, a * b = b * a for all a,b ԑ G.

So group G is abelian.


4. If ( G, ㅇ) is a group, then the group equation xx = x has a unique solution x = e.


x o x = x

Or, x o x = x o e, where e is the identity element of G.

By left cancellation law, we have,

 x = e.

Since, identity element of a group is unique, so, x = e is a unique solution of given group equation.

5. If G is a group such that (ab)^2 = a^2.b^2 for all a, b Є G, prove that G is an abelian group.


To prove that G is an abelian group, we need to show that for any elements a and b in G, the operation (binary operation in G) is commutative, i.e., ab=ba; .

Given: (ab)2=a2b2 for all a,bG


Let a,bG be arbitrary elements of the group.

From the given condition, we have: (ab)2=a2b2

Expanding the left-hand side of the equation: (ab)2=abab=a2b2

Since (ab)2=a2b2, we can cancel a from the left and b from the right side of the equation:


Thus, for any elements a and b in G, we have ab=ba, which means that G is an abelian group.

Elementary Group Theory - Exercise 3.4 : Class 12 Math PDF


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