How to calculate Perimeter and Area of ​​a triangle in Class?

Question

C++ / C#

spoiler

class Point {
    protected:
        double x, y;
    public:
        Point(double x = 0, double y = 0) 
        {
            this->x = x;
            this->y = y;
        }    
        ~Point() {}
        
        double getX() {
            return x;
        }
        double getY() {
            return y;
        }
        
        void setX(double x) {
            this->x = x; 
        }
        void setY(double y) {
            this->y = y;
        }
};

class Line: public Point {
    private:
        Point a;
    public:
        Line(Point a,Point b): Point(b) {
            this->a = a;
        }
        ~Line() {}
        
        Point getA() {
            return a;
        }
        
        void setA(Point a) {
            this->a = a;
        }
        
        double lineLength() {
            double L = sqrt(pow(a.getX() - getX(), 2) + pow(a.getY() - getY(), 2)); 
            return L;
        }
};

class Triangle: public Point {
    private:
        Point a, b;
    public:
        Triangle(Point a, Point b): Point(c)
        {
            this->a = a;
            this->b = b;
        }
        ~Triangle() {}
        
        Point getA() {
            return a;
        }
        Point getB() {
            return b;
        }
        
        void setA(Point a) {
            this->a = a;
        }
        void setB(Point b) {
            this->b = b;
        }

        double Area() {
            
        }
        double Perimeter() {
            
        }
};

There is a Triangle class that inherited the Point class.
Now you can create a triangle from three points, but how to calculate their
Perimeter P \u003d a + b + c and Area S \u003d 1/2 * ah?
Or maybe you need to create a triangle through Line and calculate its perimeter, if so, how? can be an example.

Answer 1

Inheritance implies an "is" relationship. Is the line a point? No. Is a triangle a point? No. So why the hell are you inheriting them like that? A triangle is three points. And not any, but three different points that do not lie on one straight line. The triangle must satisfy these invariants.
Area and perimeter are calculated from three points.