Algebra/Chapter 9/Completing the Square

Square Root Is Not Negative

We often say that ${\sqrt {x}}$ is the positive number, which when squared is equal to $x$. If $x>0$ this is perfectly correct, but if $x=0$ then ${\sqrt {x}}={\sqrt {0}}=0$ which is not positive. So to be technically correct (which is part of the fun of math) we should say that ${\sqrt {x}}$ is the non-negative number, which when squared is equal to $x$.

If it is needed to express that a square root may be both positive and negative, you will see $\pm {\sqrt {x}}$.