Answer
$30a^{4}$
Work Step by Step
$\sqrt 45 a^{7} \times \sqrt 20a$
We multiply the two square roots and bring them together under one square root
$\sqrt (45 a^{7} \times 20a)$
We multiply the variables together and the numbers together
$\sqrt (45\times 20 \times a^{7} \times a)$
$\sqrt (900 a^{8})$
***Square root of 900 is 30 because 30 x 30 =900
***Square root of $a^{8}$ is $a^{4}$ because $a^{4}$ x $a^{4}$ =$a^{8}$
$30a^{4}$
