public function f(ball:Point, wall:Point):Point

{

        var a:Number = (ball.x * wall.x + ball.y * wall.y) / (ball.length * wall.length);

        var k:Number = 2* (ball.length * a / wall.length);

        return new Point(wall.x*k - ball.x, wall.y*k - ball.y);

}

public function f(ball:Point, wall:Point):Point

{

        var k:Number = 2* (ball.x * wall.x + ball.y * wall.y) / (wall.x*wall.x + wall.y*wall.y);

        return new Point(wall.x*k - ball.x, wall.y*k - ball.y);

}