Cosine Documentation

Here is some of the documentation (find this on the Web with a search for "Java cos"):

java.lang 
Class Math

... 

cos

public static double cos(double a)

Returns the trigonometric cosine of an angle.

cos is a static function of the class Math, which is found in the java.lang package. Classes from that package (such as String and Math) are so common that you do not have to import the package. The angle a is a double and must be expressed in radians. The return value is a double.