Answer
$10x^2$
Work Step by Step
Use the rule $\sqrt[n]{a} \cdot \sqrt[n]{b}=\sqrt[n]{a\cdot b}$ to obtain:
$\sqrt{5x}\sqrt{20x^3}=\sqrt{5x\cdot 20x^3}$
Simplify.
$=\sqrt{100x^4}$
Use $100=10^2$ and $x^4=(x^2)^2$.
$=\sqrt{10^2(x^2)^2}$
Simplify using $\sqrt{a^2}=a, a>0$ to obtain:.
$=10x^2$
Hence, the correct answer is $10x^2$.
