To Apply a Perpendicular Constraint

Select the Constrain Elements tool.
In the tool settings window, set Method to Smart Constrain Elements by selecting the first icon.
Select the first line or ellipse.
Select the second line or ellipse.
The perpendicular constraint is displayed, and the lines are trimmed at their intersection. An attempt is made to solve and remove one degree of freedom.

Note: To override or force a perpendicular constraint, set Method to Constrain Two Lines to be Perpendicular by selecting the third icon in the tool settings window.