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# acos

Arc cosine function View other versions (4)

## 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 . acosl and acosf are the long double and the float versions, correspondingly.

The complex inverse cosine is defined by:

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

DOSUNIXWindowsANSI CC++ only
acoslâ€¢â€¢
Real acosâ€¢â€¢â€¢â€¢
Complex acosâ€¢â€¢â€¢
Complex cacosâ€¢â€¢