(PHP 4, PHP 5)
sqrt — Square root
$arg
    )
   Returns the square root of arg.
  
argThe argument to process
   The square root of arg
   or the special value NAN for negative numbers.
  
Example #1 sqrt() example
<?php
// Precision depends on your precision directive
echo sqrt(9); // 3
echo sqrt(10); // 3.16227766 ...
?>