sqrt(x) function returns the square root of x (x>=0). The return value may be an integer or float depending on the parameter. If x is a negative number or a string, it returns NAN.

<?PHP
	echo sqrt(2);  //1.4142135623731
	echo sqrt(2.5);  //1.5811388300842
	echo sqrt(-2.5);  //NAN
	echo sqrt("7429");  //NAN
	echo sqrt(3);  //1.7320508075689
	echo sqrt(4);  //2
?>

The following code can calculate the square root of a numeric array.

<?PHP
	$arr = array("2","3.4","5.342","0","3","54","6.3");
	for ($ii=0;$ii<count($arr);$ii++)
	{
		$arr[$ii] = sqrt($arr[$ii]);
	}
	print_r($arr);
?>

//the result is:
Array
(
    [0] => 1.4142135623731
    [1] => 1.8439088914586
    [2] => 2.3112767034693
    [3] => 0
    [4] => 1.7320508075689
    [5] => 7.3484692283495
    [6] => 2.5099800796022
)