In mathematics, a square root of a number x is another number that, when multiplied by itself (squared), becomes x. When it is non-negative, it is represented by the symbol \displaystyle{ \sqrt{x} }, and called the principal square root of x. For example, 3 is the square root of 9, because 3×3=9. Only numbers bigger than or equal to zero have real square roots. The only square root of zero is zero.