How to calculate pi in PHP.

pi.php

<?php

$add = true;
$pi = 3;

for ($x = 2; $x <10000; $x += 2) {
   $new = 4/($x * ($x + 1) * ($x + 2));
   $pi = $add ? 
      $pi + $new :
      $pi - $new;
   $add = !$add;
}

echo $pi . "<br>";

echo 3.14159265359;
      

Outputs:

3.1415926535918
3.14159265359