(PCC)[PHP] How to check Invalid calculation will return a NaN value in php

(PCC)::[How-to-check-Invalid-calculation-will-return-a-NaN-value-in-php]::[php]

<!DOCTYPE html>
<html>
<body>

<?php
// Invalid calculation will return a NaN value
$x = acos(8);
var_dump($x);
?>  

</body>
</html>