You have numbers in degrees but want to use the trigonometric functions.
Use deg2rad( ) and rad2deg( ) on your input and output:
$cosine = cos(deg2rad($degree));
By definition, 360 degrees is equal to 2Π radians, so it's easy to manually convert between the two formats. However, these functions use PHP's internal value of Π, so you're assured a high-precision answer. To access this number for other calculations, use the constant M_PI, which is 3.14159265358979323846.
There is no built-in support for radians. This is considered a feature, not a bug.
2.13.4. See Also
Recipe 2.12 for trig basics; documentation on deg2rad( ) at http://www.php.net/deg2rad and rad2deg( ) at http://www.php.net/rad2deg .