For calculate the area of a pentagon, **“a”** and **“r”** **length** must be known.

You see a triangle in the bottom picture. After calculating the area of the triangle, the area of the pentagon can be found by multiplying with 5.

C# Code:

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class Program { static void Main(string[] args) { double a, r, area, perimeter; Console.Write("input the border length: "); a = Convert.ToDouble(Console.ReadLine()); Console.Write("input radius (r): "); r = Convert.ToDouble(Console.ReadLine()); area = 5 * ((a * r) / 2); perimeter = 5 * a; Console.WriteLine("Pentagon perimeter : {0}", perimeter); Console.WriteLine("Pentagon area : {0}", area); Console.ReadKey(); } } |

**Output:**