Graph Functions:
dnn.epcc.edu/Student/Tutorial/Mathcenter/.../graphinglineqquadeq/graphinglinequadeqws.pps
http://funbasedlearning.com/algebra/graphing/lines/default.htm
http://www.ltcconline.net/greenl/java/BasicAlgebra/LineGraph/LineGraph.htm
http://www.mathgoodies.com/lessons/graphs/line.html
http://www.onlinemathlearning.com/graphing-lines-2.html
http://mathforum.org/cgraph/cslope/slope.html (read examples)