Answer
$\dfrac{25b-7a^3}{5a^2b}$
Work Step by Step
The $LCD$ in the given expression, $
\dfrac{5}{a^2b}-\dfrac{7a}{5b^2}
,$ is $
5a^2b^2
.$ Expressing the terms to equivalent fractions that use the $LCD$ as denominator results to
\begin{align*}\require{cancel}
&
\dfrac{5}{a^2b}\cdot\dfrac{5b}{5b}-\dfrac{7a}{5b^2}\cdot\dfrac{a^2}{a^2}
\\\\&=
\dfrac{25b}{5a^2b}-\dfrac{7a^3}{5a^2b^2}
\\\\&=
\dfrac{25b-7a^3}{5a^2b}
.\end{align*}
Hence, the given expression simplifies to $
\dfrac{25b-7a^3}{5a^2b}
.$
