php if pow -4 echo da _GET _GET echo form action index php method get

<?php

if((pow($a, 2)-4*$b*$c)>0) {
	echo "da";
}
$a = $_GET['a'];
$b = $_GET['b'];
$c = $a + $b;
//echo $c;
?>
<form action="index.php" method="get">
	<input name="a" type="text" value="<?php echo $a; ?>" size="3" maxlength="3" />
	+
	<input name="b" type="text" value="<?php echo $b; ?>" size="3" maxlength="3" />
	<input name="calc" type="submit" value="=" />
	<input name="c" type="text" value="<?php echo $c; ?>" size="5" disabled="disabled" />
</form>