PHP atan2( ) Function

The atan2() function is a builtin function in PHP and is used to calculate the arc tangent of two variables x and y passed to it as arguments.
The function returns the result in radians, which is between -Pi and Pi (inclusive).

Syntax:

float atan2($y, $x)

Parameters: This function accepts two parameters and are described below:

$y: This parameter specifies the dividend.
$x: This parameter specifies the divisor.

Return Value: It returns a float value which is the arc tangent of y/x in radians.

Examples:

Input : atan2(0.50, 0.50)
Output : 0.78539816339745

Input : atan2(-0.50, -0.50)
Output : -2.3561944901923

Input : atan2(5, 5) 
Output : 0.78539816339745

Input : atan2(10, 20) 
Output : 0.46364760900081

Below programs, taking different values of the parameters are used to illustrate the atan2() function in PHP:

When (0.50, 0.50) is passed as a parameter:

<?php

echo (atan2(0.50, 0.50));

?>
Output:
```
0.78539816339745
```
When (-0.50, -0.50) is passed as a parameter:

<?php

echo (atan2(-0.50, -0.50));

?>
Output:
```
-2.3561944901923
```
When (5, 5) is passed as a parameter:

<?php

echo (atan2(5, 5));

?>
Output:
```
0.78539816339745
```
When (10, 20) is passed as a parameter:

<?php

echo (atan2(10, 20));

?>
Output:
```
0.46364760900081
```