Change of operators in denominator, stuck for one hour: why in the world is there an addition sign there?

[coooool222]

Can someone please tell me why in the world there's an addition sign there.
Im guessing since its going to negative infinity the radical value itself is negative but the negatives cancel out to be positive.
Please help.

 

[Harry_the_cat]

If \(\displaystyle x\) is negative, as it is here, then \(\displaystyle x=-\sqrt {x^2}\).