---
tag: 0F7FQS6XY6
kind: concept
name: Square root
msc: [26A09]
sources:
  - url: https://en.wikipedia.org/wiki/Square_root
    locator: lead section
same_as:
  wikidata: Q134237
  wikipedia: Square root
---

## Summary

A square root of a number $x$ is a number $y$ with $y^2 = x$.
Each nonnegative real number $x$ has exactly one nonnegative square root, the principal square root $\sqrt{x}$.
For example, $\sqrt{9} = 3$, and the square roots of $9$ are $3$ and $-3$.