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Parallel lines
From Greek: para allelois "beside one another"
Lines are parallel if they lie in the same plane, and are the same distance apart over their entire length
Try this Drag any orange dot at the points P or Q. As the line
(If there is no image below, see support page.)
PQ
moves, the line
 RS will remain parallel to it.
Parallel lines remain the same distance apart over their entire length. No matter how far you extend them, they will never meet. The arrows
To show that lines are parallel, we draw small arrow marks on them.
In the figure above, note the arrows on the lines
PQ
and
RS .
This shows that these lines are parallel.
If the diagram has another set of parallel lines they would have two arrows each, and so on.
Shorthand notation
When we write about parallel lines there is a shorthand we can use. We can write
PQ || RS .
which
is read as "the line PQ is parallel to the line RS".
Constructing a parallel line
In the Constructions chapter, there is an animated demonstration of how to construct
a line parallel to another that passes through a given point, using only a compass and straightedge.
See Constructing a parallel line through a point.
Other parallel topicsGeneralAngles associated with parallel lines
(C) 2008 Copyright John Page
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