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# atan2

Arc tangent function of two variables
View other versions (4)

## Interface

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

## Description

The atan2 function computes the principal value of the arc tangent of y / x, using the signs of both arguments to determine the quadrant of the return value. It produces correct results even when the resulting angle is near or (for x near 0).

Example:

##### Example - Arc tangent function of two variables
Workings
#include <stdio.h>
#include <math.h>
int main(void)
{
double result, x = 90.0, y = 15.0;
result = atan2(y, x);
printf("The arc tangent ratio of %lf is %lf\n", (y/x), result);
return 0;
}
Solution
Output:

The arc tangent ratio of 0.166667 is 0.165149

## Special Values

atan2 ( ±0, -0 ) returns ±.

atan2 ( ±0, +0 ) returns ±0.

atan2 ( ±0, x ) returns ± for x < 0.

atan2 ( ±0, x ) returns ±0 for x > 0.

atan2 ( ±0 ) returns for y > 0.

atan2 ( ±y, -∞ ) returns ± for finite y > 0.

atan2 ( ±y, +∞ ) returns ±0 for finite y > 0.

atan2 ( ±∞, +x ) returns ± for finite x

atan2 ( ±∞, -∞ ) returns ±.

atan2 ( ±∞, +∞ ) returns ±.

## Notes

The atan2 function is used mostly to convert from rectangular (x,y) to polar (r, ) coordinates that must satisfy and . In general, conversions to polar coordinates should be computed thus:

## Standards

The atan2 function conforms to ISO/IEC 9899:1999(E).