COS(): cosine of the num parameter

<?Php
echo COS(PI()); // Output is -1
echo "<br>";
echo COS(PI()/2); // Output  6.1232339957368E-17 // Same as 0 
echo "<br>";
echo COS(PI()/3); // Output is 0.5
echo "<br>";
echo COS(PI()/4); // Output is 0.70710678118655 
?>

COS(X);

deg2rad() with COS()

<?Php
echo cos(deg2rad(0)); // Output  is 1
echo "<br>";
echo cos(deg2rad(180)); // Output  is -1
?>

Plotting of SIN & COS curves by using PHP GD function with deg2rad()