Definition of Parallel Lines
How many lines can you draw parallel to a line at a point not on the line? Let P be a point and l be a line not containing point P.
There is only one line through point P that is parallel to line l.
Postulate. Parallel Postulate
There is exactly one line parallel to a line at a given point not contained on the line.
The Parallel Postulate establishes the existence and uniqueness of a line parallel to another line passing through a given point not on the line.
Refer to the given figure below. Are the three lines parallel?
Line m is parallel to line l and line n is also parallel to line l.
What can you conclude about lines m and n?
Two lines parallel to the same line are parallel.
