http://www.ck12.org Chapter 3. Parallel and Perpendicular Lines
For a line and a point not on the line, there is exactly one line parallel to this line through the point. There are
infinitely many lines that pass throughA, but only one is parallel tol.
Skew linesare lines that are in different planes and never intersect. The difference between parallel lines and skew
lines is parallel lines lie in the same plane while skew lines lie in different planes.
Atransversalis a line that intersects two distinct lines. These two lines may or may not be parallel. The area
between landmis the called theinterior. The areaoutside landmis called theexterior.
TheParallel Lines Propertyis a transitive property that can be applied to parallel lines. It states that if linesl||m
andm||n, thenl||n.
Example A
Are linesqandrparallel?
Notice that the arrow markings indicate thatp||q. Similarly, arrow markings indicate thatp||r. This means that
q||rby the Parallel Lines Property.
Example B
In the cube below, list 3 pairs of parallel planes.