- pow: documentation ( source)
<?php
$p = 0;
$i = 0.06;
$c = 12;
$n = 1;
$r = 200;
$x = $i / $c;
$y = pow((1 + $x), ($n * $c));
$vf = $p * $y + (($r * $y - 1) / $x); // your original equation
echo $vf;
echo "\n\n";
$vf = $p * $y + ($r * ($y - 1) / $x); // correct equation
echo $vf;