Is the power of 1/2 same thing as principal square root? $\sqrt{9} = 3$
9 has 2 square roots: 3 and -3.
What is $9^\frac12$? Is $9^\frac12 = \sqrt{9} = 3$ or is $9^\frac12 = \pm3$?

$a^b$ is always positive for $a\in\Bbb R^+$ and $b\in\Bbb R$.  This is because $f(x)=a^x$ satisfies the functional equation $f(x+y)=f(x)f(y)$ (i.e. $a^{x+y}=a^xa^y$).  It follows that $f(2x)=f(x)^2,$ or $$a^x=f(x)=f\left(\frac x2\right)^2\ge 0$$
Consequently, $9^\frac12\ge 0\implies 9^\frac12=3$
