Causes selected lines to lie 90 degrees to one another.
Access Methods
Button
Toolbar: Drafting tool set 
Parametric tool group Geometric Constraints flyout Perpendicular Menu:
Parametric
Geometric Constraints
Perpendicular
Summary
This command is equivalent to the Perpendicular option in GEOMCONSTRAINT.
Lines do not have to intersect to be perpendicular.
Following are the valid constraint objects and points:
- Line
- Polyline segment
- Ellipse
- Multiline text