Relationships Between 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.

Symbol

The relationship of perpendicularity between two lines is written using the symbol "[latex]\perp[/latex]" and is read "is perpendicular to".

Example

droites_perpendiculaires The figure shows [latex]\mathit{l}_{1}\perp \mathit{l}_{2}[/latex]. 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 [latex]\perp[/latex] as the symbol for perpendicularity in his book Cursus Mathematicus in 1634.

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