Calculating Distance between two Latitude and Longitude GeoCoordinates

gistfile1.cs

public static double Calculate(double sLatitude,double sLongitude, double eLatitude, 
                               double eLongitude)
{
    var sLatitudeRadians = sLatitude * (Math.PI / 180.0);
    var sLongitudeRadians = sLongitude * (Math.PI / 180.0);
    var eLatitudeRadians = eLatitude * (Math.PI / 180.0);
    var eLongitudeRadians = eLongitude * (Math.PI / 180.0);

    var dLongitude = eLongitudeRadians - sLongitudeRadians;
    var dLatitude = eLatitudeRadians - sLatitudeRadians;

    var result1 = Math.Pow(Math.Sin(dLatitude / 2.0), 2.0) + 
                  Math.Cos(sLatitudeRadians) * Math.Cos(eLatitudeRadians) * 
                  Math.Pow(Math.Sin(dLongitude / 2.0), 2.0);

    // Using 3956 as the number of miles around the earth
    var result2 = 3956.0 * 2.0 * 
                  Math.Atan2(Math.Sqrt(result1), Math.Sqrt(1.0 - result1));

    return result2;
}

gistfile2.cs

var sCoord = new GeoCoordinate(sLatitude, sLongitude);
var eCoord = new GeoCoordinate(eLatitude, eLongitude);

return sCoord.DistanceTo(eCoord);

gistfile3.cs

function distanceTo(lat1, lon1, lat2, lon2, unit) {
      var rlat1 = Math.PI * lat1/180
      var rlat2 = Math.PI * lat2/180
      var rlon1 = Math.PI * lon1/180
      var rlon2 = Math.PI * lon2/180
      var theta = lon1-lon2
      var rtheta = Math.PI * theta/180
      var dist = Math.sin(rlat1) * Math.sin(rlat2) + Math.cos(rlat1) * Math.cos(rlat2) * Math.cos(rtheta);
      dist = Math.acos(dist)
      dist = dist * 180/Math.PI
      dist = dist * 60 * 1.1515
      if (unit=="K") { dist = dist * 1.609344 }
      if (unit=="N") { dist = dist * 0.8684 }
      return dist
}