Undoing a Square

To solve $x^{2} = 25$, find the numbers whose square is 25. There are two of them, 5 and -5, because $5^{2} = 25$ and $\left(-5\right)^{2} = 25$. Taking the square root of both sides gives both solutions, written $x = \pm 5$.

A positive number and its negative have the same square. So undoing a square always gives two cases, $x = 5$ or $x = -5$. The symbol ± is a short way to write both cases in one line.

When the right side is positive, always include both square roots, the positive one and the negative one. Take the square root of the squared side to get the two cases, then solve each case on its own.