We can write √(x2) as ..."the absolute value of x" = l x l
And the absolute value of any number is either 0 (in the case of 0, itself), or a positive number.
So let x = a where a > 0 and rearranging your equation, we have
l a l + a = 0
a + a = 0 which is impossible, since adding two postives can never = 0
So let x = 0
l 0 l + 0 = 0
0 + 0 = 0 ....and x = 0 is OK
Now, let x =a where a < 0
l a l + a = 0
-a + a = 0 ....note that, if a < 0, then the absolute value of a is just -a...and this is OK, too. (For example,
l -3 l = 3.........so if a = -3, then -a = 3.
So the answer to your question is that....... x ≤ 0.