public double DienTich()
{
double p = ChuVi() / 2;
return(Math.Sqrt((p - DiemA.KhoangCach(DiemB)) * (p - DiemA.KhoangCach(DiemC)) * (p - DiemB.KhoangCach(DiemC))));
}
public double ChuVi()
{
return(DiemA.KhoangCach(DiemB) + DiemA.KhoangCach(DiemC) + DiemB.KhoangCach(DiemC));
}