To Apply a Perpendicular 2D Constraint

Select the Perpendicular 2D Constraint tool.
Select a linear or an elliptical segment.
Select another linear or an elliptical segment.
The two selected segments are now perpendicular to each other. In case of elliptical segment, the axis of the ellipse participates in the process.

Note: For two segments to be perpendicular, they must be on the same plane.