Answer
$-4x(x+3)(x-3)$
Work Step by Step
The factored form of the expression, $
\dfrac{x}{x^2-9}
,$ is
\begin{array}{l}\require{cancel}
\dfrac{x}{(x+3)(x-3)}
.\end{array}
The factored form of the expression, $
\dfrac{5}{x}
,$ is
\begin{array}{l}\require{cancel}
\dfrac{5}{x}
.\end{array}
The factored form of the expression, $
\dfrac{7}{12-4x}
,$ is
\begin{array}{l}\require{cancel}
\dfrac{7}{-(4x-12)}
\\\\
\dfrac{7}{-4(x-3)}
\\\\
-\dfrac{7}{4(x-3)}
.\end{array}
Hence, the $LCD$ of the given expressions is
\begin{array}{l}\require{cancel}
-4x(x+3)(x-3)
.\end{array}
