Originally Posted by
alyosha2 In textbook
$\displaystyle r(ar) = ar^2$
but
$\displaystyle r(ar) = rarr = ar^3$
the r does not distribute over multiplication like it does for addition ...
$\displaystyle \textcolor{red}{r(ar) = r(ra) = (rr) a = r^2a = ar^2}$