# Group theory Q (1 Viewer)

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#### ElDavidas

"What is the order of a group G generated by elements a and b subject only to the relations

$$a^7 = 1$$ , $$b^3 = 1$$ , $$ba = a^rb$$"

I know that the order is the number of elements in the group.

I'm having a lot of trouble answering a lot of these questions.
Any help would be greatly appreciated.

#### Hurkyl

Staff Emeritus
Gold Member
Well, you could always write down all of the elements of the group.

#### ElDavidas

Hurkyl said:
Well, you could always write down all of the elements of the group.
How do you go about doing that using the information given? I don't know where to begin.

Also, does $a^7 = 1$ mean a to the 7 is equal to the identity element?

#### Hurkyl

Staff Emeritus
Gold Member
Well, there's a, and aa, and aaa, and ab, and ba, and aba, and bab, and abbaabbab, and...

Yes, the relation a^7 = 1 means that aaaaaaa is the identity.

#### ElDavidas

I think I see where this is going.

Does $a^8 = a^7 * a = 1 * a$ make sense?

#### topsquark

ElDavidas said:
I think I see where this is going.

Does $a^8 = a^7 * a = 1 * a$ make sense?
Yup. And use the ba relation to reorder your products so that they all read "aaaa....bb..."

-Dan

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