The square root of a number is a value that when multiplied by itself gives the original number.
√x is defined as the non-negative number whose square equals x. The radical symbol √ denotes the principal (non-negative) square root. Roots can be square (√), cube (³√), or any nth root (ⁿ√). Square roots of negative numbers produce imaginary numbers (√-1 = i). Roots appear in the quadratic formula, Pythagorean theorem, and many areas of algebra, geometry, and physics.
The square root concept dates to ancient Babylon (1800 BCE) who had methods to approximate √2. The radical symbol √ was first used by Christoff Rudolff in 1525. The symbol likely comes from the letter "r" for "radix" (Latin for root).