Answer
$\dfrac{5(a+2)}{3(a-5)(a+5)}$
Work Step by Step
The expression $
\dfrac{2}{3a-15}-\dfrac{a}{25-a^2}
$ simplifies to
\begin{array}{l}
\dfrac{2}{3(a-5)}-\dfrac{a}{(5+a)(5-a)}
\\\\=
\dfrac{2}{3(a-5)}+\dfrac{a}{(5+a)(a-5)}
\\\\=
\dfrac{2(a+5)+3a}{3(a-5)(a+5)}
\\\\=
\dfrac{2a+10+3a}{3(a-5)(a+5)}
\\\\=
\dfrac{5a+10}{3(a-5)(a+5)}
\\\\=
\dfrac{5(a+2)}{3(a-5)(a+5)}
.\end{array}
