using System;

public class Program

{

    public static void Main()

    {

        //var areaOfEquilateralTriangle = 

    }

}

​

public interface IShape {}

​

public interface ITriangle : IShape{

    double side1 {get; set;}

    double side2 {get; set;}

    double side3 {get; set;}

    double Area(double side1, double side2, double side3);

}

​

​

public class Equilateral : ITriangle {

    public double side1 {get; set;}

    public double side2 {get; set;}

    public double side3 {get; set;}

    public double Area(double side1, double side2, double side3){

        return Math.Pow(side1, 2) * (Math.Sqrt(3) / 4);

    }

}

​

​

​