public EllipticArcBuilderEx( 
   Segment segment1,
   Segment segment2,
   double radius,
   Coordinate2D hintPoint,
   SpatialReference spatialReference
)

// Construct a segment from (100, 100) to (50, 50) and another segment from (100, 100) to (150, 50).
// Use a builderEx convenience method or use a builderEx constructor.

LineSegment segment1 = LineBuilderEx.CreateLineSegment(new Coordinate2D(100, 100), new Coordinate2D(50, 50));
LineSegment segment2 = LineBuilderEx.CreateLineSegment(new Coordinate2D(100, 100), new Coordinate2D(150, 50));

// Construct the hint point to determine where the arc will be constructed.
Coordinate2D hintPoint = new Coordinate2D(100, 75);

// Call QueryFilletRadius to get the minimum and maximum radii that can be used with these segments.
var minMaxRadii = EllipticArcBuilderEx.QueryFilletRadiusRange(segment1, segment2, hintPoint);

// Use the maximum radius to create the arc.
double maxRadius = minMaxRadii.Item2;

// BuilderEx convenience methods don't need to run on the MCT.
//At 2.x - EllipticArcSegment circularArc = EllipticArcBuilderEx.CreateEllipticArcSegment(segment1, segment2, maxRadius, hintPoint);
EllipticArcSegment circularArc = EllipticArcBuilderEx.CreateCircularArc(
                    segment1, segment2, maxRadius, hintPoint);

// This EllipticArcBuilderEx constructor needs to run on the MCT either.
EllipticArcBuilderEx cab = new EllipticArcBuilderEx(segment1, segment2, maxRadius, hintPoint);
EllipticArcSegment otherCircularArc = cab.ToSegment();

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D center = new Coordinate2D(4.5, 4);
var eabCir = new EllipticArcBuilderEx(center, 0.5, ArcOrientation.ArcClockwise);
var cir = eabCir.ToSegment();

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

//Set symbolology, create and add element to layout
CIMTextSymbol sym = SymbolFactory.Instance.ConstructTextSymbol(
                ColorFactory.Instance.GreenRGB, 10, "Arial", "Regular");
string text = "Circle, circle, circle";

GraphicElement cirTxtElm = ElementFactory.Instance.CreateTextGraphicElement(
  container, TextType.CircleParagraph, poly, sym, text, "New Circle Text", false);