Find and Invert Normal of a curve

How can I do to find and reverse the normal of a curve in C#?

Technically, curves do not have normals. What you are seeing is the tangent direction.

If you are using C++, you want want to use these:

ON_Curve::TangentAt()
ON_Curve::Reverse()

If you are using C# and RhinoCommon, you want to use these:

Rhino.Geometry.Curve.TangentAt()
Rhino.Geometry.Curve.Reverse()

Great Help!
Thanks