# Is my non-commutative algebra correct?

• Dec 21st 2011, 04:56 PM
beebe
Is my non-commutative algebra correct?
Doing algebra without the normal commuting rules is super unintuitive for me. Did I do this right?

"If G is a group and $\displaystyle g,h \in G$, write $\displaystyle (gh)^{-1}$ in terms of $\displaystyle g^{-1}$ and $\displaystyle h^{-1}$"

What I did (I'm doing all of my operations on the right hand side):

$\displaystyle (gh)^{-1}(gh)=e$
$\displaystyle (gh)^{-1}(ghh^{-1})=h^{-1}$
$\displaystyle (gh)^{-1}(gg^{-1})=h^{-1}g^{-1}$
$\displaystyle (gh)^{-1}=h^{-1}g^{-1}$

Is that right? It seems weird to me that splitting the h and g would make them switch places.
• Dec 21st 2011, 05:20 PM
Deveno
Re: Is my non-commutative algebra correct?
your algebra is correct. you can think of it this way:

when you take off your shoes and socks, you do it in the opposite order as you put them on.
• Dec 21st 2011, 05:29 PM
beebe
Re: Is my non-commutative algebra correct?
Thanks!

Ick, that tex was awful. My bad.