Offset/Mirror
Offset or mirror a sketch curve.
Mirror
Create symmetric copies of selected sketch curves across a selected centerline. By default, there is a parent-child relationship between source curves and their symmetric copies.
- 
                On the ribbon Sketch ribbon, select the
                        Mirror tool.

 - Select the sketch entities to mirror.
 - On the guide bar, select Axis.
 - Select an axis or line as the centerline to mirror across.
 - Select Apply on the guide bar or microdialog.
 - Right-click and mouse through the check mark to exit, or double-right-click.
 
Offset
Create a copy of a sketch curve at a specified distance from the source curve.