csharp-3/extension-methods/PointExtensions.cs - The static class PointExtensions.

Lecture 5 - slide 28 : 29 Program 3

using System;

public static class PointExtensions{   

  public static double DistanceTo(this Point p1, Point p2){   
    return Math.Sqrt((p1.X - p2.X) * (p1.X - p2.X) +          
                     (p1.Y - p2.Y) * (p1.Y - p2.Y));          
  }                                                           

}