Square root
![The mathematical expression](/Images/godic/202502/12/Nuvola_apps_edu_mathematics_blue-p.svg5605.png")
![The graph of the function f(x) = √x, made up of half a parabola with a vertical directrix.](/Images/godic/202502/12/Square_root_0_25.svg5605.png")
![First leaf of the complex square rootSecond leaf of the complex square rootUsing the Riemann surface of the square root, it is shown how the two leaves fit together](/Images/godic/202502/12/Complex_sqrt_leaf15605.jpg")
![](/Images/godic/202502/12/Complex_sqrt_leaf25605.jpg")
In mathematics, a square root of a number a is a number y such that y = a, in other words, a number y whose square (the result of multiplying the number by itself, or y × y) is a. For example, 4 and −4 are square roots of 16 because 4 = (−4) = 16.
Every non-negative real number a has a unique non-negative square root, called the principal square root, which is denoted by √a, where √ is called the radical sign or radix. For example, the principal square root of 9 is 3, denoted √9 = 3, because 3 = 3 × 3 = 9 and 3 is non-negative. The term whose root is being considered is known as the radicand. The radicand is the number or expression underneath the radical sign, in this example 9.