Sketch a curve that connects to the end of an existing line.
Select a tool that allows for an arc.
Click Modify | Place Lines tab (or respective Modify | Place <Element> tab or Modify | Create <Element> tab)Draw panel (Tangent End Arc), and place the cursor in the drawing area.
Click the endpoint of an existing wall or line to specify the start point for the tangent arc.
Move the cursor and click to specify the end point of the arc.