### atan - atan2 -- Calculate Arctangent

Format

>     #include <math.h>
>     double atan(double x);
>     double atan2(double y, double x);

Language Level: ANSI, POSIX, XPG4
atan and atan2 calculate the arctangent of x and y/x, respectively.

Return Value
atan returns a value in the range -PI/2 to PI/2 radians. atan2 returns a value in the range -PI to PI radians. If both arguments of atan2 are zero, the function sets errno to EDOM, and returns a value of 0.

Example
This example calculates arctangents using the atan and atan2 functions.

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

    int main(void)
    {
        double a,b,c,d;

        c = 0.45;
        d = 0.23;

        a = atan(c);
        b = atan2(c,d);

        printf("atan( %lf ) = %lf\n", c, a);
        printf("atan2( %lf, %lf ) = %lf\n", c, d, b);
        return 0;

       /************************************************
          The output should be:

          atan( 0.450000 ) = 0.422854
          atan2( 0.450000, 0.230000 ) = 1.098299
       ************************************************/
    }

acos -- Calculate Arccosine
asin -- Calculate Arcsine
cos -- Calculate Cosine
cosh -- Calculate Hyperbolic Cosine
_fpatan -- Calculate Arctangent
_fptan -- Calculate Tangent
sin -- Calculate Sine
sinh -- Calculate Hyperbolic Sine
tan -- Calculate Tangent
tanh -- Calculate Hyperbolic Tangent
<math.h>