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acos, acosl

Header File

math.h

Category

Math Routines

Prototype

double acos(double x);

long double acosl(long double x);

Description

Calculates the arc cosine.

acos returns the arc cosine of the input value.

acosl is the long double version; it takes a long double argument and returns a long double result.

Arguments to acos and acosl must be in the range -1 to 1, or else acos and acosl return NAN and set the global variable errno to:

EDOM Domain error

Return Value

acos and acosl of an argument between -1 and +1 return a value in the range 0 to pi. Error handling for these routines can be modified through the functions _matherr_matherr and _matherrl.

Example

Copy Code

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

Portability

| POSIX | Win32 | ANSI C | ANSI C++
acos | + | + | + | +
acosl |  | + | + | +

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