Parallel & Perpendicular Lines
Sources
Gloag, Anne and Andrew "Writing Linear Equations", CK-12 Foundation's Algebra FlexBook, December 9, 2009, http://www.ck12.org/flexr/flexbook/738/
Holt, Rinehart, & Winston. "Linear Functions." http://my.hrw.com/
math06_07/nsmedia/homework_help/alg1/alg1_ch05_08_
homeworkhelp.html (accessed August 14, 2010).