question: private Point2D rotate ( Point2D a , Point2D center , double angle ) { double resultX = center . getX ( ) + ( a . getX ( ) - center . getX ( ) ) * Math . cos ( angle ) - ( a . getY ( ) - center . getY ( ) ) * Math . sin ( angle ) ; double resultY = center . getY ( ) + ( a . getX ( ) - center . getX ( ) ) * Math . sin ( angle ) + ( a . getY ( ) - center . getY ( ) ) * Math . cos ( angle ) ; return new Point2D ( resultX , resultY ) ; }
target:  * Util methods	                                                            *