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Synopsis:
    #include <math.h>
    double acos( double x );

Description:
    The acos function computes the principal value of the arccosine of x.  A
    domain error occurs for arguments not in the range [-1,1].

Returns:
    The acos function returns the arccosine in the range [0,P].  When the
    argument is outside the permissible range, the  matherr function is
    called.  Unless the default  matherr function is replaced, it will set
    the global variable  errno to  EDOM, and print a "DOMAIN error"
    diagnostic message using the  stderr stream.

See Also:
    asin, atan, atan2, matherr

Example:
    #include <stdio.h>
    #include <math.h>

    void main()
      {
        printf( "%f\n", acos(.5) );
      }

    produces the following:

    1.047197

Classification:
    ANSI

Systems:
    All