In geometry, the perpendicular symbol is used to show that two lines are perpendicular to each other. Typically, perpendicular lines are written in an expression like this:
In plain language, this means the line is perpendicular to the line . The lines corresponding to this expression can be drawn in a figure like this:
A line is written as two letters with a double-headed arrow overtop, where the letters name two points the line passes through.
Parallel lines are denoted by the parallel symbol placed between the notation of the two lines. A line is denoted by the start and end letter with a line over top.