A good answer might be:

Both are double.

Cosine Documentation

Here is some of the documentation:

cos

public static double cos(double a)

Returns the trigonometric cosine of an angle.

Looking further through the documentation uncovers that the angle a must be expressed in radians. This is so common in math and programming that the initial documentation does not mention it.

QUESTION 17:

(Math Review: ) Can angles in radian mesure be converted to degrees?