# What is the LCD between x/(x^2 - 81 ) and (3x)/(x^2+18x +81)?

$\frac{x}{{x}^{2} - 81} = \frac{x}{\textcolor{red}{\left(x + 9\right)} \textcolor{g r e e n}{\left(x - 9\right)}}$
$\frac{3 x}{{x}^{2} + 18 x + 81} = \frac{3 x}{\textcolor{red}{\left(x + 9\right)} \textcolor{b l u e}{\left(x + 9\right)}}$
${\left(x + 9\right)}^{2} \left(9 - x\right)$