public override DatumTransformation GetInverse()

// Create singleton from wkid
CompositeGeographicTransformation cgt = 
    ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(108272);
int count = cgt.Count;    // count = 1

IList<GeographicTransformation> gts = cgt.Transformations 
                                as IList<GeographicTransformation>;
gts.Add(ArcGIS.Core.Geometry.GeographicTransformation.Create(1437, false));
count = cgt.Count;        // count = 2

// create from an enumeration
CompositeGeographicTransformation another_cgt = 
              ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(gts);
GeographicTransformation gt0 = another_cgt[0];
GeographicTransformation gt1 = another_cgt[1];

// get the inverse
CompositeGeographicTransformation inversed_cgt = another_cgt.GetInverse() as CompositeGeographicTransformation;
// inversed_cgt[0] is same as gt1
// inversed_cgt[1] is same as gt0

var wkt = gt0.Wkt;
// create from string 
CompositeGeographicTransformation third_cgt = 
   ArcGIS.Core.Geometry.CompositeGeographicTransformation.Create(wkt, gt0.IsForward);
count = third_cgt.Count;        // count = 1

// create from josn
string json = cgt.ToJson();
CompositeGeographicTransformation joson_cgt = 
  DatumTransformation.CreateFromJson(json) as CompositeGeographicTransformation;