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

The complex inverse cosine is defined by:

Example 1:

#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;
}

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.

See Also

sin, cos, tan, asin, atan, atan2, sinh, cosh, tanh

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		•			•

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