Answer
$\dfrac{3}{10+5\sqrt{7}}$
Work Step by Step
Multiplying by the conjugate of the numerator, then the rationalized-numerator form of the given expression, $
\dfrac{2-\sqrt{7}}{-5}
,$ is
\begin{array}{l}\require{cancel}
\dfrac{2-\sqrt{7}}{-5}\cdot\dfrac{2+\sqrt{7}}{2+\sqrt{7}}
\\\\=
\dfrac{(2)^2-(\sqrt{7})^2}{-5(2)-5(\sqrt{7})}
\\\\=
\dfrac{4-7}{-10-5\sqrt{7}}
\\\\=
\dfrac{-3}{-10-5\sqrt{7}}
\\\\=
\dfrac{-(3)}{-(10+5\sqrt{7})}
\\\\=
\dfrac{3}{10+5\sqrt{7}}
.\end{array}
