3．　　声明一个名为Rectangle的矩形类，其属性为矩形的左下角和右上角两点的坐标，并有友元函数计算矩形的周长及面积。编程实现求左下角与右上角坐标分别为（2.1，3.2），（5.2，6.3）的矩形周长及面积。并编写一个友元类，类中的成员函数实现坐标点的显示。-3. Declare a class named Rectangle rectangle, and its property to the lower left and upper right corner of the rectangle coordinates of two points, and a friend function to calculate the perimeter and area of ​ ​ a rectangle. Programming and seek lower-left corner right corner coordinates are (2.1,3.2), (5.2,6.3) rectangular perimeter and area. And the preparation of a friend class, class member functions to display the coordinates of the point.