acos


function
<cmath> 
     double acos (      double x );
      float acos (       float x );
long double acos ( long double x );

Compute arc cosine

Returns the principal value of the arc cosine of x, expressed in radians.

In trigonometrics, arc cosine is the inverse operation of cosine.

In C++, this function is overloaded in <valarray> (see valarray acos).

Parameters

x
Floating point value in the interval [-1,+1].
If the argument is out of this interval, a domain error occurs, setting the global variable errno to the value EDOM.


Return Value

Principal arc cosine of x, in the interval [0,pi] radians.

Portability

In C, only the double version of this function exists with this name.

Example

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/* acos example */
#include <stdio.h>
#include <math.h>

#define PI 3.14159265

int main ()
{
  double param, result;
  param = 0.5;
  result = acos (param) * 180.0 / PI;
  printf ("The arc cosine of %lf is %lf degrees.\n", param, result );
  return 0;
}


Output:

The arc cosine of 0.500000 is 60.000000 degrees.


See also

cos Compute cosine (function)
asin Compute arc sine (function)