Copy and paste this symbol: √
Windows: press `Alt` + `251` on the numeric keypad
Mac: press `Option` + `V`
In Microsoft Word: type `221A`, then press `Alt` + `X`
On many phones: long-press the `0` or use the symbols keyboard to find `√`
In HTML: use `√` or `√`
In LaTeX: type `sqrt{}`
In Google Docs: go to `Insert` > `Special characters` and search for `square root`