What the square root symbol means
The square root of a number is the value that, multiplied by itself, gives that number: √9 = 3 because 3 × 3 = 9. The sign √ is called the radical, and the number under it is the radicand. In India, √2 is usually read aloud as "under root 2", which is why many people search for the under root symbol.
Handy values to remember: √4 = 2, √16 = 4, √100 = 10, √2 ≈ 1.414 and √3 ≈ 1.732. √ always means the positive (principal) root, so √9 is 3, not −3. To show both solutions of x² = 9, write x = ±3 with the plus minus symbol.
The sign first appeared in print in 1525 in a book by the German mathematician Christoph Rudolff, and it is often said to come from a stylized letter r, for the Latin radix (root). René Descartes later joined it to the bar across the top.
How to type √ on any device
On a Mac, press Option + V. On Windows, hold Alt and type 251 on the number pad. In Microsoft Word, type 221A and press Alt + X, or press Alt + = to start an equation and type \sqrt. In Google Docs, choose Insert > Equation and type \sqrt.
On Android with Gboard, √ is on the second symbols page (?123, then =\<). In LaTeX, write \sqrt{x} for √x and \sqrt[3]{x} for a cube root. In HTML, use √. In Excel and Google Sheets, the function is =SQRT(16), which returns 4.
The bar over the number
Plain text cannot draw the long bar (vinculum) that stretches over the radicand, so use parentheses to show what is under the root: √(x + 1) is not the same as √x + 1. For a properly drawn root, use the equation editor in Word, Google Docs or LaTeX.
Unicode has single characters for the cube root symbol ∛ and the fourth root ∜. For higher roots, put a superscript number in front of √, like ⁵√32 = 2.