#### Answer

$\sqrt{35ab}$

#### Work Step by Step

Using the Product Rule of radicals which is given by $\sqrt[m]{x}\cdot\sqrt[m]{y}=\sqrt[m]{xy},$ the given expression is equivalent to
\begin{array}{l}\require{cancel}
\sqrt{5a}\sqrt{7b}
\\\\=
\sqrt{5a(7b)}
\\\\=
\sqrt{35ab}
.\end{array}