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:

1. $y: This parameter specifies the dividend.
2. $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

Reference:
http://php.net/manual/en/function.atan2.php