public static CubicBezierSegment CreateCubicBezierSegment( 
   MapPoint startPoint,
   Coordinate2D controlPoint1,
   Coordinate2D controlPoint2,
   MapPoint endPoint,
   SpatialReference spatialReference
)

{
  // Use a builderEx convenience method or a builderEx constructor.

  MapPoint startPt = MapPointBuilderEx.CreateMapPoint(1.0, 1.0, 3.0);
  MapPoint endPt = MapPointBuilderEx.CreateMapPoint(2.0, 2.0, 3.0);

  Coordinate2D ctrl1Pt = new Coordinate2D(1.0, 2.0);
  Coordinate2D ctrl2Pt = new Coordinate2D(2.0, 1.0);

  // BuilderEx convenience methods don't need to run on the MCT
  CubicBezierSegment bezier = CubicBezierBuilderEx.CreateCubicBezierSegment(startPt, ctrl1Pt, ctrl2Pt, endPt, SpatialReferences.WGS84);

  // without a SR
  bezier = CubicBezierBuilderEx.CreateCubicBezierSegment(startPt, ctrl1Pt, ctrl2Pt, endPt);


  // builderEx constructors don't need to run on the MCT
  CubicBezierBuilderEx cbbEx = new CubicBezierBuilderEx(startPt, ctrl1Pt, ctrl2Pt, endPt);
  bezier = cbbEx.ToSegment() as CubicBezierSegment;

  // another alternative
  cbbEx = new CubicBezierBuilderEx(startPt, ctrl1Pt.ToMapPoint(), ctrl2Pt.ToMapPoint(), endPt);
  bezier = cbbEx.ToSegment() as CubicBezierSegment;
}

{
  //Note: Must be on QueuedTask.Run
  //Build geometry
  Coordinate2D pt1 = new Coordinate2D(1, 7.5);
  Coordinate2D pt2 = new Coordinate2D(1.66, 8);
  Coordinate2D pt3 = new Coordinate2D(2.33, 7.1);
  Coordinate2D pt4 = new Coordinate2D(3, 7.5);
  var bez = new CubicBezierBuilderEx(pt1, pt2, pt3, pt4);
  var bezSeg = bez.ToSegment();
  Polyline bezPl = PolylineBuilderEx.CreatePolyline(bezSeg, AttributeFlags.AllAttributes);

  //Set symbology, create and add element to layout
  CIMLineSymbol lineSym = SymbolFactory.Instance.ConstructLineSymbol(
    ColorFactory.Instance.RedRGB, 4.0, SimpleLineStyle.DashDot);

  ElementFactory.Instance.CreateGraphicElement(layout, bezPl, lineSym, "New Bezier");
}