Square root
In mathematics, a
square root of a number
a is a number
y such that
y2 =
a, in other words, a number
y whose
square is
a. For example, 4 and −4 are square roots of 16 because 42 = 2 = 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 32 = 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. Every positive number
a has two square roots: √
a, which is positive, and −√
a, which is negative. Together, these two roots are denoted ± √
a. Although the principal square root of a positive number is only one of its two square roots, the designation "
the square root" is often used to refer to the
principal square root.