Here’s an example of how to draw pentagons with C#.

//http://mathworld.wolfram.com/Pentagon.html
namespace M1
{
    using System;
    using System.Drawing;
    using System.Drawing.Drawing2D;
    using System.Drawing.Imaging;

    public static class Program
    {
        #region Constants

        private static readonly double C1 = 0.25d * (Math.Sqrt(5d) - 1d);
        private static readonly double C2 = 0.25d * (Math.Sqrt(5d) + 1d);
        private static readonly byte[] PentagonPathPointTypes = { 0, 1, 1, 1, 129 };
        private static readonly double S1 = 0.25d * Math.Sqrt(10d + 2d * Math.Sqrt(5d));
        private static readonly double S2 = 0.25d * Math.Sqrt(10d - 2d * Math.Sqrt(5d));

        #endregion Constants
        
        #region Methods

        private static GraphicsPath CreatePentagon(PointF center, float radius)
        {
            var s1 = S1 * radius;
            var s2 = S2 * radius;
            var c1 = C1 * radius;
            var c2 = C2 * radius;
            var point0 = new PointF(center.X, center.Y - radius);
            var point1 = new PointF((float)(center.X + s1), (float)(center.Y - c1));
            var point2 = new PointF((float)(center.X + s2), (float)(center.Y + c2));
            var point3 = new PointF((float)(center.X - s2), (float)(center.Y + c2));
            var point4 = new PointF((float)(center.X - s1), (float)(center.Y - c1));
            var pts = new[] { point0, point1, point2, point3, point4 };
            return new GraphicsPath(pts, PentagonPathPointTypes);
        }

        #endregion Methods

        private static void Main(string[] args)
        {
            using (var bitmap = new Bitmap(1000, 1000))
            {
                using (var graphics = Graphics.FromImage(bitmap))
                {
                    graphics.Clear(Color.White);
                    graphics.SmoothingMode = SmoothingMode.HighQuality;
                    var center = new PointF(bitmap.Width / 2, bitmap.Height / 2);
                    var radius = 200f;
                    var pentagon = CreatePentagon(center, radius);
                    graphics.FillPath(Brushes.Yellow, pentagon);
                    graphics.DrawEllipse(Pens.Green, center.X - radius, center.Y - radius, radius * 2, radius * 2);
                }
                bitmap.Save(@"pentagon.jpg", ImageFormat.Jpeg);
            }
        }
    }
}