# asin man page

asin, asinf, asinl — arc sine function

## Synopsis

#include <math.h> double asin(doublex); float asinf(floatx); long double asinl(long doublex);

`Link with `

*-lm*.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

**asinf**(), **asinl**():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

## Description

These functions calculate the principal value of the arc sine of *x*; that is the value whose sine is *x*.

## Return Value

On success, these functions return the principal value of the arc sine of *x* in radians; the return value is in the range [-pi/2, pi/2].

If *x* is a NaN, a NaN is returned.

If *x* is +0 (-0), +0 (-0) is returned.

If *x* is outside the range [-1, 1], a domain error occurs, and a NaN is returned.

## Errors

See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

- Domain error:
*x*is outside the range [-1, 1] *errno*is set to**EDOM**. An invalid floating-point exception (**FE_INVALID**) is raised.

## Attributes

For an explanation of the terms used in this section, see attributes(7).

Interface | Attribute | Value |
---|---|---|

asin(), asinf(), asinl() | Thread safety | MT-Safe |

## Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning *double* also conforms to SVr4, 4.3BSD, C89.

## See Also

acos(3), atan(3), atan2(3), casin(3), cos(3), sin(3), tan(3)

## Colophon

This page is part of release 4.15 of the Linux *man-pages* project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

## Referenced By

acos(3), atan(3), atan2(3), cos(3), sin(3), tan(3).

The man pages asinf(3) and asinl(3) are aliases of asin(3).