Inequalities-Section 3.3
Given an inequality, graph it (then check), OR given graph, find the inequality (then check).
For a video explanation, see
https://www.khanacademy.org/math/algebra/linear-equations-and-inequalitie/graphing-linear-inequalities/v/graphing-inequalities
or http://patrickjmt.com/graphing-systems-of-linear-inequalities-example-1/
or http://patrickjmt.com/graphing-systems-of-linear-inequalities-example-2/