Click Bisecting Line
in the Profile toolbar (Line sub-toolbar).
Click two points on both lines, one after the other.
The infinite bisecting line automatically appears, in
accordance with both points previously clicked.
Tip:
This
bisecting line corresponds to a line symmetrically constrained
to two lines on the condition that GeometricalConstraint
is active in the Sketch tools toolbar. If both selected
lines are parallel to each others, a new line will be created
between these lines.