Definition: The Cos () Function, calculates the cosine of the given number and returns it in radians. It is written as Cos (your_number) ;
Also Known As: Cosine, Cos
Examples:
<?php
echo cos(M_PI) ;
?>
This returns a value of -1
By Angela Bradley, About.com Guide
<?php
echo cos(M_PI) ;
?>
This returns a value of -1