1. ## simplification

In textbook
$r(ar) = ar^2$

but

$r(ar) = rarr = ar^3$

what?

2. Originally Posted by alyosha2
In textbook
$r(ar) = ar^2$

but

$r(ar) = rarr = ar^3$

the r does not distribute over multiplication like it does for addition ...

$\textcolor{red}{r(ar) = r(ra) = (rr) a = r^2a = ar^2}$
..

3. Originally Posted by alyosha2
In textbook
$r(ar) = ar^2$

but

$r(ar) = rarr = ar^3$

what?
$r(ar)\neq ar^3$

4. so how do you geot from $r(ar)$ to $ar^2$?

5. Originally Posted by alyosha2
so how do you geot from $r(ar)$ to $ar^2$?
$r(ar) = a(rr) = ar^2$