Помогите решить задачу в C++

 #include  

#include  

#include  

using namespace std; 

struct Dot { 

    double x; 

    double y; 

    double length(const Dot& d)const { 

        return sqrt(pow(d.x - x, 2) + pow(d.y - y, 2)); 

    } 

private: 

    friend istream& operator>>(istream& inp, Dot& d) { 

        return inp >> d.x >> d.y; 

    } 

}; 

class Triangle { 

    Dot da, db, dc; 

    friend istream& operator>>(istream& inp, Triangle& t) { 

        return inp >> t.da >> t.db >> t.dc; 

    } 

    tuple lengths()const { 

        const auto a = da.length(db); 

        const auto b = db.length(dc); 

        const auto c = dc.length(da); 

        return { a, b, c }; 

    } 

    double argument()const { 

        const auto [a, b, c] = lengths(); 

        auto p = (a + b + c) / 2.0; 

        return p * (p - a) * (p - b) * (p - c); 

    } 

public: 

    bool exist()const { 

        argument() > 0; 

    } 

    bool equilateral_triangle()const { 

        static const auto eps = 1e-12; 

        const auto [a, b, c] = lengths(); 

        return fabs(a - b) < eps && fabs(b - c) < eps && fabs(c - a) < eps; 

    } 

}; 

int main() { 

    Triangle tr; 

    cin >> tr; 

    if (tr.exist()) { 

        puts("Triangle exist."); 

        if (tr.equilateral_triangle()) { 

            puts("Equilateral triangle."); 

        } 

    } else { 

        puts("Triangle not exist."); 

    } 

}