#### Answer

$(\sqrt x)^{2}$ = x
$10b^{2} $

#### Work Step by Step

$(\sqrt x)^{2}$ = x
$2b ( \sqrt 5b)^{2}$
= $2b ( \sqrt 5b) \times ( \sqrt 5b)$
Since ( \sqrt 5b) and ( \sqrt 5b) are under a square root we multiply them together under a square root
= $2b ( \sqrt (5b \times 5b))$
= $2b ( \sqrt (25b^{2}))$
Square root of $25b^{2}$ is 5b because 5b x 5b = $25b^{2}$
= 2b ( 5b)
We multiply the numbers together and variables together
= $10b^{2} $