The GNU C Library
19.3 Inverse Trigonometric Functions
These are the usual arc sine, arc cosine and arc tangent functions,
which are the inverses of the sine, cosine and tangent functions
respectively.
 Function: double asin (double x)

 Function: float asinf (float x)

 Function: long double asinl (long double x)
 These functions compute the arc sine of xthat is, the value whose
sine is x. The value is in units of radians. Mathematically,
there are infinitely many such values; the one actually returned is the
one between
pi/2
and pi/2
(inclusive).
The arc sine function is defined mathematically only
over the domain 1
to 1
. If x is outside the
domain, asin
signals a domain error.
 Function: double acos (double x)

 Function: float acosf (float x)

 Function: long double acosl (long double x)
 These functions compute the arc cosine of xthat is, the value
whose cosine is x. The value is in units of radians.
Mathematically, there are infinitely many such values; the one actually
returned is the one between
0
and pi
(inclusive).
The arc cosine function is defined mathematically only
over the domain 1
to 1
. If x is outside the
domain, acos
signals a domain error.
 Function: double atan (double x)

 Function: float atanf (float x)

 Function: long double atanl (long double x)
 These functions compute the arc tangent of xthat is, the value
whose tangent is x. The value is in units of radians.
Mathematically, there are infinitely many such values; the one actually
returned is the one between
pi/2
and pi/2
(inclusive).
 Function: double atan2 (double y, double x)

 Function: float atan2f (float y, float x)

 Function: long double atan2l (long double y, long double x)
 This function computes the arc tangent of y/x, but the signs
of both arguments are used to determine the quadrant of the result, and
x is permitted to be zero. The return value is given in radians
and is in the range
pi
to pi
, inclusive.
If x and y are coordinates of a point in the plane,
atan2
returns the signed angle between the line from the origin
to that point and the xaxis. Thus, atan2
is useful for
converting Cartesian coordinates to polar coordinates. (To compute the
radial coordinate, use hypot
; see 19.4 Exponentiation and Logarithms.)
If both x and y are zero, atan2
returns zero.
ISO C99 defines complex versions of the inverse trig functions.
 Function: complex double casin (complex double z)

 Function: complex float casinf (complex float z)

 Function: complex long double casinl (complex long double z)
 These functions compute the complex arc sine of zthat is, the
value whose sine is z. The value returned is in radians.
Unlike the realvalued functions, casin
is defined for all
values of z.
 Function: complex double cacos (complex double z)

 Function: complex float cacosf (complex float z)

 Function: complex long double cacosl (complex long double z)
 These functions compute the complex arc cosine of zthat is, the
value whose cosine is z. The value returned is in radians.
Unlike the realvalued functions, cacos
is defined for all
values of z.
 Function: complex double catan (complex double z)

 Function: complex float catanf (complex float z)

 Function: complex long double catanl (complex long double z)
 These functions compute the complex arc tangent of zthat is,
the value whose tangent is z. The value is in units of radians.