## NAME

asin, asinf, asinl − arc sine function

## SYNOPSIS

**#include
<math.h>**

**double
asin(double** *x***);
float asinf(float**

*x*

**);**

long double asinl(long double

long double asinl(long double

*x*

**);**

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).

## 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 4.16 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/.