Video: https://www.youtube.com/watch?v=5h6YzRRxzO4
Notes: http://www.algebra-class.com/graphing-inequalities.html
Quiz: https://www.sophia.org/concepts/graphing-linear-inequalities-in-two-variables--2
Gizmos Interactive: https://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=142
Examples http://catalog.flatworldknowledge.com/bookhub/128?e=fwk-redden-ch03_s08