The square root of a (necessarily) positive number is always positive: $\sqrt {a^2} = a$ if $a \ge 0$ $\sqrt {a^2} = -a$ if $a \le 0$ $\sqrt {a^2} = \vert a \vert $ (absolute value of a !)

Go !

$\LARGE \sqrt{(-3)^2} =$	$\LARGE \vert-3\vert = -(-3) = 3$
$\LARGE \sqrt{-3}$	is no real number because $\LARGE -3\lt 0 $
$\LARGE \sqrt{a^4}=$	$\LARGE \vert a^2 \vert = a^2 \qquad$ because   $\LARGE a^2 \ge 0$