atan2

Calculates the inverse tangent of a quotient

```#include <math.h>
double atan2 ( double y , double x  );
float atan2f ( float y , float x  );         (C99)
long double atan2l ( long double y , long double x  );         (C99)
```

The atan2( ) function divides the first argument by the second and returns the arc tangent of the result, or arctan(y/x).

The return value is given in radians, and is in the range -p atan2(y,x) p. The signs of x and y determine the quadrant of the result:

x > 0, y > 0:

0 atan2( y,x) p/2

x < 0, y > 0:

p/2 atan2( y,x) p

x < 0, y < 0:

-p atan2( y,x) -p/2

x > 0, y < 0:

-p/2 atan2( y,x) 0

If both arguments are zero, then the function may incur a domain error.

#### Example

```/*
* Calculate an acute angle of a right triangle, given
* the adjacent and opposite sides.
*/
#define PI 3.141593

double adjacent = 3.0;
double opposite = 4.0;
double angle = atan2( opposite, adjacent ) * DEG_PER_RAD;

printf( "The acute angles of a 3-4-5 right triangle are %4.2f\xB0 "
"and %4.2f\xB0.\n", angle, 90.0 - angle );
```

This code produces the following output:

```The acute angles of a 3-4-5 right triangle are 53.13° and 36.87°.
```