Класс EquilateralTriangle

using System;
namespace example
{
    public class Program
    {
        static void Main(string[] args)
        {
            do {
                Console.Write(" Введите четырёхзначное число от 1 до 4: ");
                ushort data = ushort.Parse(Console.ReadLine());
                EquilateralTriangle et = new EquilateralTriangle();
                double param;
                bool control = true;

                switch (data)
                {
                    case 1:
                        Console.Write(" Введите сторону: ");
                        param = double.Parse(Console.ReadLine());
                        et.SetSide(param);
                        break;
                    case 2:
                        Console.Write(" Введите радиус вписанной окружности: ");
                        param = double.Parse(Console.ReadLine());
                        et.SetRadiusIn(param);
                        break;
                    case 3:
                        Console.Write(" Введите описанной окружности: ");
                        param = double.Parse(Console.ReadLine());
                        et.SetRadiusOut(param);
                        break;
                    case 4:
                        Console.Write(" Введите площадь треугольника: ");
                        param = double.Parse(Console.ReadLine());
                        et.SetArea(param);
                        break;
                    default:
                        Console.WriteLine(" Ошибка!");
                        control = false;
                        break;
                }

                if (control)
                {
                    Console.WriteLine(" 1 - {0}\n 2 - {1}\n 3 - {2}\n 4 - {3}",
                        et.GetSide(), et.GetRadiusIn(), et.GetRadiusOut(), et.GetArea());
                    Console.ReadKey();
                }
            } while (true);
        }
    }

    public class EquilateralTriangle
    {
        private double side;
        private double radiusIn;
        private double radiusOut;
        private double area;

        public EquilateralTriangle()
        {
            side = radiusIn = radiusOut = area = 0;
        }

        public void SetSide(double _side)
        {
            side = Math.Abs(_side);
            CalculateRadiusInFromSide();
            CalculateRadiusOutFromSide();
            CalculateAreaFromSide();
        }

        public void SetRadiusIn(double _radiusIn)
        {
            radiusIn = Math.Abs(_radiusIn);
            CalculateSideFromRadiusIn();
            CalculateRadiusOutFromRadiusIn();
            CalculateAreaFromRadiusIn();
        }

        public void SetRadiusOut(double _radiusOut)
        {
            radiusOut = Math.Abs(_radiusOut);
            CalculateSideFromRadiusOut();
            CalculateRadiusInFromRadiusOut();
            CalculateAreaFromRadiusOut();
        }

        public void SetArea(double _area)
        {
            area = Math.Abs(_area);
            CalculateSideFromArea();
            CalculateRadiusInFromArea();
            CalculateRadiusOutFromArea();
        }

        public double GetSide()
        {
            return side;
        }

        public double GetRadiusIn()
        {
            return radiusIn;
        }

        public double GetRadiusOut()
        {
            return radiusOut;
        }

        public double GetArea()
        {
            return area;
        }

        private void CalculateSideFromRadiusIn()
        {
            side = radiusIn / (Math.Sqrt(3.0) / 6);
        }

        private void CalculateSideFromRadiusOut()
        {
            side = radiusOut / (Math.Sqrt(3.0) / 3);
        }

        private void CalculateSideFromArea()
        {
            side = Math.Sqrt(area / (Math.Sqrt(3.0) / 4));
        }

        private void CalculateRadiusInFromSide()
        {
            radiusIn = Math.Sqrt(3.0) / 6 * side;
        }

        private void CalculateRadiusInFromRadiusOut()
        {
            radiusIn = radiusOut / 2;
        }

        private void CalculateRadiusInFromArea()
        {
            CalculateSideFromArea();
            CalculateRadiusInFromSide();
        }

        private void CalculateRadiusOutFromSide()
        {
            radiusOut = Math.Sqrt(3.0) / 3 * side;
        }

        private void CalculateRadiusOutFromRadiusIn()
        {
            radiusOut = radiusIn * 2;
        }

        private void CalculateRadiusOutFromArea()
        {
            CalculateSideFromArea();
            CalculateRadiusOutFromSide();
        }

        private void CalculateAreaFromSide()
        {
            area = Math.Sqrt(3.0) / 4 * Math.Pow(side, 2);
        }

        private void CalculateAreaFromRadiusIn()
        {
            CalculateRadiusInFromSide();
            CalculateAreaFromSide();
        }

        private void CalculateAreaFromRadiusOut()
        {
            CalculateSideFromRadiusOut();
            CalculateAreaFromSide();
        }
    }
}