ArcGIS Pro 2.7 API Reference Guide
IsCircular Property (EllipticArcBuilder)
Example 

ArcGIS.Core.Geometry Namespace > EllipticArcBuilder Class : IsCircular Property
Gets if this elliptical arc is actually circular (that is major and minor axes have the same length). This method must be called on the MCT. Use QueuedTask.Run.
Syntax
public bool IsCircular {get;}
Public ReadOnly Property IsCircular As Boolean
Exceptions
ExceptionDescription
This method or property must be called within the lambda passed to QueuedTask.Run.
Example
// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  // retrieve the curve's control points
  using (EllipticArcBuilder builder = new EllipticArcBuilder(arcSegment))
  {
    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;
    esriArcOrientation orientation = builder.Orientation;
  }
});
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

EllipticArcBuilder Class
EllipticArcBuilder Members