Answer
$21|x|-7\sqrt{5x}+15\sqrt{x}-5\sqrt{5}$
Work Step by Step
Using $(a+b)(c+d)=ab+ad+bc+bd$ or the FOIL Method, the expression $
\left( 7\sqrt{x}+5 \right)\left( 3\sqrt{x}-\sqrt{5} \right)
$ simplifies to
\begin{array}{l}
7\sqrt{x}\left( 3\sqrt{x} \right)+7\sqrt{x}\left( -\sqrt{5} \right)+5\left( 3\sqrt{x} \right)+5\left( -\sqrt{5} \right)
\\\\=
21\sqrt{x^2}-7\sqrt{5x}+15\sqrt{x}-5\sqrt{5}
\\\\=
21|x|-7\sqrt{5x}+15\sqrt{x}-5\sqrt{5}
.\end{array}
