PHP Pythagorean Theorem Function

I got a bit bored today, so I decided to write a simple function to mock the function of the Pythagorean Theorem.

<?php
function pythagorean ($a, $b, $c) {
	(!$a) ? $out = sqrt($c * $c - $b * $b) : null;
	(!$b) ? $out = sqrt($c * $c - $a * $a) : null;
	(!$c) ? $out = sqrt($a * $a + $b * $b) : null;
	return $out;
}
?>

Using the function, you can find the hypotenuse when you know the legs are 3 and 4 using the following snippet of code:

echo pythagorean(3, 4, false);

Feel free to use it however you wish. You might also want to round the answer to the nearest integer using:

echo round(pythagorean(3, 4, false));