Calculate: 9r^3-12r^2-9r

Expression: $9r^{3}-12r^{2}-9r$

Apply exponent rule $a^{b+c}=a^{b}a^{c}$

$=9r^{2}r-12rr-9r$

Rewrite $9$ as $3\cdot 3$

$=3\cdot 3r^{2}r-3\cdot 4rr-3\cdot 3r$

Factor out common term $3r$

$=3r(3r^{2}-4r-3)$