If the square root of a variable is negative, as shown below:
$$\sqrt x = -1$$
Then what is $x$ equal to? The closest answer I can think of is $i^4$.
$$\sqrt{i^4}=i^{\frac42}=i^2=-1$$
But if $i^4$ is evaluated first, then it doesn't work:
$$\sqrt{i^4}=\sqrt{(-1)(-1)}=\sqrt1=1$$