public EllipticArcBuilderEx( 
   EllipticArcSegment ellipticArc,
   SpatialReference spatialReference
)

{
  // retrieve the curve's properties
  EllipticArcBuilderEx builder = new EllipticArcBuilderEx(ellipticArcSegment);
  MapPoint startPt = builder.StartPoint;
  MapPoint endPt = builder.EndPoint;
  Coordinate2D centerPt = builder.CenterPoint;
  bool isCircular = builder.IsCircular;
  bool isMinor = builder.IsMinor;
  double startAngle = builder.StartAngle;
  double endAngle = builder.EndAngle;
  double centralAngle = builder.CentralAngle;
  double rotationAngle = builder.RotationAngle;
  ArcOrientation orientation = builder.Orientation;
}

{
  //Note: Must be on QueuedTask.Run

  //Build geometry
  Coordinate2D center = new Coordinate2D(4.5, 2.75);
  var eabElp = new EllipticArcBuilderEx(center, 0, 1, 0.45, ArcOrientation.ArcClockwise);
  var ellipse = eabElp.ToSegment();

  var poly = PolygonBuilderEx.CreatePolygon(
    PolylineBuilderEx.CreatePolyline(ellipse, AttributeFlags.AllAttributes));

  //Set symbology, create and add element to layout
  CIMTextSymbol sym = SymbolFactory.Instance.ConstructTextSymbol(
                        ColorFactory.Instance.BlueRGB, 10, "Arial", "Regular");
  string text = "Ellipse, ellipse, ellipse";

  GraphicElement ge = ElementFactory.Instance.CreateTextGraphicElement(
    layout, TextType.PolygonParagraph, poly, sym, text, "New Ellipse Text", false);
}

{
  //Note: Must be on QueuedTask.Run

  //Build geometry
  Coordinate2D center = new Coordinate2D(2, 2.75);
  var eabElp = new EllipticArcBuilderEx(
                           center, 0, 1, 0.45, ArcOrientation.ArcClockwise);
  var ellipse = eabElp.ToSegment();

  //Set symbology, create and add element to layout
  CIMStroke outline = SymbolFactory.Instance.ConstructStroke(
                        ColorFactory.Instance.GreenRGB, 2.0, SimpleLineStyle.Dot);
  CIMPolygonSymbol ellipseSym = SymbolFactory.Instance.ConstructPolygonSymbol(
                   ColorFactory.Instance.GreyRGB, SimpleFillStyle.Vertical, outline);

  var poly = PolygonBuilderEx.CreatePolygon(
    PolylineBuilderEx.CreatePolyline(ellipse, AttributeFlags.AllAttributes));

  var ge = ElementFactory.Instance.CreatePredefinedShapeGraphicElement(
    layout, PredefinedShape.Ellipse, poly.Extent.Center, 0, 0, ellipseSym,
    "New Ellipse2", false, new ElementInfo() { Anchor = Anchor.TopRightCorner });
}