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# C math atan2() function

### C math atan2() function

The C library function double atan2(double y, double x) is used to return the arc tangent in radians of y/x based on the signs of both values to determine the correct quadrant. It takes two arguments: x-coordinate and y-coordinate, and calculate the angle in radians for the quadrant. This function is defined in <math.h> header file.

Syntax:
`double atan2(double y, double x);`

### Parameters:

• x − It is the floating point value representing an x-coordinate
• y − It is the floating point value representing a y-coordinate.
Here is an example of atan2() function:
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, y, ret, val;
x = 0.75;
y = 0.555;
val = 180.0 / PI;
ret = atan2(y,x) * val;
printf("The arc tangent of x = %lf, y = %lf  is %lf", x, y,ret);
return(0);
}
```
```
Output:
The arc tangent of x = 0.750000, y = 0.555000 is 36.501441
Example-2
``````
#include <stdio.h>
#include <math.h>
#define PI 3.14159265
int main ()
{
double x, y, ret, val;
x = 0.75;
y = -0.555;
val = 180.0 / PI;
ret = atan2(y,x) * val;
printf("The arc tangent of x = %lf, y = %lf  is %lf", x, y,ret);
return(0);
}
```
```
Output:
The arc tangent of x = 0.750000, y = -0.555000 is -36.501441