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Computing › C › Math.h ›

acos

Arc cosine function

View other versions (4)

Contents

Interface
Description
Special Values
See Also
Standards
Compatibility
Page Comments

Interface

#include <math.h>double  acos (double x)
long double  acosl (long double x)
float  acosf (float x)

#include <complex.h>complex  acos (complex x)
double complex  cacos (double complex x)
float complex  cacosf (float complex x)
long double complex  cacosl (long double complex x)

Description

The acos function computes the principal value of the arc cosine of x in the range $[0, \pi]$ . acosl and acosf are the long double and the float versions, correspondingly.

The complex inverse cosine is defined by:

$\mathrm{acos}(x) = -i \log \left( x+ i \sqrt{1-x^2} \right).$

(1)

Example:

Example - Arc cosine function

Problem

This is an example of finding arc cosine of x

Workings

#include <stdio.h>
#include <math.h>
int main()
{
  double x = 0.5;
  double result = acos(x);
  printf("The arc cosine of %lf is %lf\n", x, result);
  return 0;
}

Solution

Output:

The arc cosine of 0.500000 is 1.047198

Special Values

acos ( 1 ) returns +0.
acos ( x ) returns a NaN and raises the invalid floating-point exception for |x| > 1.

Standards

The acos function conforms to ISO/IEC 9899:1999(E).

Compatibility

	DOS	UNIX	Windows	ANSI C	C++ only
acosl	•		•
Real acos	•	•	•	•
Complex acos	•		•		•
Complex cacos		•			•

Page Comments

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double	`acos` (double x)
long double	`acosl` (long double x)
float	`acosf` (float x)

complex	`acos` (complex x)
double complex	`cacos` (double complex x)
float complex	`cacosf` (float complex x)
long double complex	`cacosl` (long double complex x)