Perpendicular Lines

Perpendicular Lines

Lines that intersect at right angles.

The relationship of perpendicularity between the lines in a geometric plane is symmetric but neither reflexive nor transitive.


The relationship of perpendicularity between two lines is written using the symbol “\(\perp\)” and is read “is perpendicular to”.



The figure shows \(\mathit{l}_{1}\perp \mathit{l}_{2}\).
In the figure, the right angle is represented by a small square in one of the angles formed by the two perpendicular lines.

Historical note

French mathematician Pierre Herigone was the first to use the symbol \(\perp\) as the symbol for perpendicularity in his book Cursus Mathematicus in 1634.

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