/ ˈskwer ˈruːt /
A number that when multiplied by itself equals a given number.
In mathematics, a number that when squared (multiplied by itself) equals a given number. For example, the square root of 25 (written Ö25) is ± 5, because 5 x 5 = 25, and (-5) x (-5) = 25. As an exponent, a square root is represented by ˝, for example, 16˝ = 4.
Negative numbers (less than 0) do not have square roots that are real numbers. Their roots are represented by complex numbers, in which the square root of -1 is given the symbol i (that is, ± i2 = -1). Thus the square root of -4 is Ö[(-1) x 4] = Ö-1 x Ö4 = 2i.