Calculate Standard Deviation of Percentages

[insert_php]

if (isset($_POST[‘Submit’]))
{

$K=$_POST[‘K’];
$a=16.97;
$b=17+$a;
$c=17-$a;

$result=(1/32)* (pow($b, $K) + pow($c, $K)-2);
echo round($result);
}
[/insert_php]