package utils  {
	
	public class Radians {

		public function Radians() {
			
		}
		
		/*	Radians to degrees	*/
		public static function toDegrees(radians:Number):Number
		{
			return radians * 180 / Math.PI;
		}
		
		/*	Degrees to radians	*/
		public static function fromDegrees(degrees:Number):Number
		{
			return degrees * Math.PI / 180;
		}
	}
}

example: posX +=  Math.cos(Radians.fromDegrees(rotation)) * speed;

Radians / Degrees Utility AS3

ActionScript 3