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 x---that 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 x---that 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 x---that 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 x-axis. 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 z---that is, the
value whose sine is z. The value returned is in radians.
Unlike the real-valued 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 z---that is, the
value whose cosine is z. The value returned is in radians.
Unlike the real-valued 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 z---that is,
the value whose tangent is z. The value is in units of radians.
