function cos( x ) {
	return addon( x );
}
Computes the cosine of a number.

@private
@param {number} x - input value (in radians)
@returns {number} cosine

@example
var v = cos( 0.0 );
// returns 1.0

@example
var v = cos( 3.141592653589793 / 4.0 );
// returns ~0.707

@example
var v = cos( -3.141592653589793 / 6.0 );
// returns ~0.866

@example
var v = cos( NaN );
// returns NaN