public EllipticArcBuilderEx( 
   MapPoint startPt,
   MapPoint endPt,
   Coordinate2D interiorPt,
   SpatialReference spatialReference
)

{
  // Construct a circular arc from (2, 1) to (1, 2) with interior pt (1 + sqrt(2)/2, 1 + sqrt(2)/2).
  // Use a builderEx convenience method or use a builderEx constructor.

  MapPoint fromPtCircArc = MapPointBuilderEx.CreateMapPoint(2, 1);
  MapPoint toPtCircArc = MapPointBuilderEx.CreateMapPoint(1, 2);
  Coordinate2D interiorPtNew = new Coordinate2D(1 + Math.Sqrt(2) / 2, 1 + Math.Sqrt(2) / 2);

  // BuilderEx convenience methods don't need to run on the MCT.
  EllipticArcSegment circularArcBuilder = EllipticArcBuilderEx.CreateCircularArc(fromPtCircArc, toPtCircArc, interiorPtNew);

  // BuilderEx constructors don't need to run on the MCT.
  EllipticArcBuilderEx eab = new EllipticArcBuilderEx(fromPtCircArc, toPtCircArc, interiorPtNew);
  // do something with the builder

  EllipticArcSegment anotherCircularArc = eab.ToSegment();
}

{
  //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 });
}