static void Main(string[] args)
        {
            var rectangle = new Rectangle(5, 12);
            Console.WriteLine("Created rectangle with (Width: {0}, Height: {1}).", rectangle.Width, rectangle.Height);

            var rotatedRectangle = Rectangle.GetRotatedRectangle(rectangle, Math.PI / 2); // PI/2 is 90 degrees
            Console.WriteLine("Rotated rectangle(90 degrees) with (Width: {0}, Height: {1}).", 
                rotatedRectangle.Width, rotatedRectangle.Height);

        }
        public static Rectangle GetRotatedRectangle(Rectangle rectangle, double angleOfRotation)
        {
            //I don't understand the expression, but tried to simplify it and make it easier to read.
            double sinus = Math.Abs(Math.Sin(angleOfRotation));
            double cosinus = Math.Abs(Math.Cos(angleOfRotation));

            double width = cosinus * rectangle.Width + sinus * rectangle.Height;
            double height = sinus * rectangle.Width + cosinus * rectangle.Height;

            return new Rectangle(width, height);
        }
        static void Main(string[] args)
        {
            //2c:
            int num1 = 1;
            int num2 = 2;
            int total = 0;

            total = num1 + num2;
            Console.WriteLine("{0} + {1} = {2}", num1, num2, total);

            //2d:
            Add(20, 30);
            //2e:
            Add(20, 30, 25);

            //2g:
            Rectangle rectangle = new Rectangle();
            rectangle.RectangleArea(3, 5);

            //2h:
            rectangle.RectangleArea(4, 5);

            Console.ReadKey();
        }