---
name: "cbrt"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/cbrt"
---

# cbrt(3)

cube root, square root, and inverse square root functions

## NAME

**cbrt**, **cbrtf**, **cbrtl**, **rsqrt**, **rsqrtf**, **rsqrtl,** **sqrt**, **sqrtf**, **sqrtl** – cube root, square root, and inverse square root functions

## LIBRARY

Math Library (libm, -lm)

## SYNOPSIS

**#include \<math.h\>**

*double*\

**cbrt**(*double x*);

*float*\

**cbrtf**(*float x*);

*long* *double*\

**cbrtl**(*long double x*);

*double*\

**rsqrt**(*double x*);

*float*\

**rsqrtf**(*float x*);

*long* *double*\

**rsqrtl**(*long double x*);

*double*\

**sqrt**(*double x*);

*float*\

**sqrtf**(*float x*);

*long* *double*\

**sqrtl**(*long double x*);

## DESCRIPTION

The **cbrt**(), **cbrtf**(), and **cbrtl**() functions compute the cube root of *x*.

The **rsqrt**(), **rsqrtf**(), and **rsqrtl**() functions compute the inverse square root of *x*.

The **sqrt**(), **sqrtf**(), and **sqrtl**() functions compute the non-negative square root of *x*.

## RETURN VALUES

The **cbrt**(), **cbrtf**(), and **cbrtl**() functions return the requested cube root.

The **rsqrt**(), **rsqrtf**(), and **rsqrtl**() functions return 1 divided by the square root of *x* unless an error occurs. An attempt to take the **rsqrt**() of negative *x* raises an invalid exception and causes an  to be returned. The inverse square root of 0 returns ∞ and raises a divide-by-zero exception.

The **sqrt**(), **sqrtf**(), and **sqrtl**() functions return the requested square root unless an error occurs. An attempt to take the **sqrt**() of negative *x* raises an invalid exception and causes an  to be returned (except that the square root of -0 is valid and equal to -0.)

## SEE ALSO

[fenv(3)](/fenv/3.md), [math(3)](/math/3.md)

## STANDARDS

The **cbrt**(), **cbrtf**(), **cbrtl**(), **sqrt**(), **sqrtf**(), and **sqrtl**() functions conform to ISO/IEC 9899:1999 (“ISO C99”). The **rsqrt**(), **rsqrtf**(), and **rsqrtl**() functions conform to ISO/IEC 9899:2024 ("ISO C23").

## HISTORY

The **cbrt**() function appeared in 4.3BSD. The **sqrt**() function appeared in Version 2 AT&T UNIX. **sqrtl**() function appeared in FreeBSD 8.0. The **cbrtl**() function appeared in FreeBSD 9.0. The **rsqrt**(), **rsqrtf**(), and **rsqrtl**() functions appeared in FreeBSD 16.0.