The $\pm$ sign definitely can cause a lot of confusion for students. For starters,

$|x|=\pm{x}$
$x^{2}={|x|}^2$

and the list goes on.

So my focus today is to explain when to put $\pm$ while dealing with $\sqrt{ }$. First, lets recognise a few things.

$x=\sqrt{9}$: This gives us $x=3$

$x^{2}=9$: This gives us $x=\pm{3}$

Yes, the square-root can be raised to a square for the x, but notice the difference in answer in both cases. The former is a $+3$ while the latter has $-3$ too. This is because the square-root is always a positive square-root and does not return $\pm{ }$. On the other hand, $x^{2}={|x|}^2$ and the $|x|=\pm{x}$ which causes the $\pm{ }$.

So next time, please be alert when you introduce the $\pm{ }$.

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