Proof about identity element of a group

In summary, in order to prove that a is the identity element of a group G, we can assume a is not the identity and use the inverse of b to show that a*b equals b. This can be done by *-ing things with the inverse of b, such as a*b*b-inverse=b*b-inverse.
  • #1
hoopsmax25
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Homework Statement


If G is a group, a is in G, and a*b=b for some b in G (* is a certain operation), prove that a is the identity element of G


Homework Equations





The Attempt at a Solution


I feel like you should assume a is not the identity element and eventually show that a= the identity. but I am not sure how to show that.
 
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  • #2
Hint: Think about using ##b^{-1}##.
 
  • #3
I thought about using the inverse of b but I'm not sure how to plug it in?
 
  • #4
You don't "plug it in". You could try *-ing things with it.
 
  • #5
Could you do a*b*b-inverse=b*b-inverse? and go from there?
 

FAQ: Proof about identity element of a group

What is the identity element of a group?

The identity element of a group is an element that, when combined with any other element in the group, results in the same element. In other words, it leaves other elements unchanged when used in a group operation. It is typically denoted as "e" or "1".

How is the identity element determined in a group?

The identity element is determined by the group's operation and its elements. It must satisfy the property that when combined with any element in the group, it results in the same element. This can be found by trial and error or through mathematical calculations.

Is the identity element unique in a group?

Yes, the identity element is unique in a group. This means that there can only be one identity element in a group, and it is the same for all elements in the group.

What is the significance of the identity element in a group?

The identity element is important in a group because it serves as the starting point for all group operations. It also helps in determining the inverse of an element and proving other properties of a group.

Can a group have more than one identity element?

No, a group cannot have more than one identity element. If a group has two distinct identity elements, then they must be equal, as the identity element is unique in a group.

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