（1）在二维平面空间上，使用x、y坐标可以确定一个点；确定了圆心坐标和半径后可以确定一个圆。声明一个点类，并使用这个点类的对象为数据成员声明圆类。

（2）设计并测试一个名为Ellipse的椭圆类，其属性为外接矩形的左上角与右下角两个点的坐标，并能计算出椭圆的面积

-(1) in two-dimensional space, using the x, y coordinates of a point can be determined　determine the center coordinates and the radius of a circle can be determined later. Declaring a Point class, and use this point as a data object of the class member declarations round classes. (2) to design and test a class named Ellipse ellipse whose property is the upper left and lower right corner of bounding rectangle coordinates of two points, and to calculate the area of ​ ​ the ellipse