Consider the following function and closed interval.

f$($x$)=($x $2)($x $8)($x $9),[2,9]$If f is differentiable on the open interval $(2,9),$ find

f$\text{'}($x$).$

$($If it is not differentiable on the open interval, enter DNE.$)$

f$\text{'}($x$)$