The mathematical purpose of this lesson is to give students a chance to name and analyze common incomplete strategies and concepts when working with inequalities. Students engage in error analysis on the topic of testing points around a given boundary to determine which half of the real number line contains solutions to an inequality, and on the topic of solving equations.

Error analysis around solving equations helps students continue to hone the foundational skill of solving equations, which is useful for finding the boundary point of the solutions of a linear inequality. Exploring the reasoning behind testing points helps students make strategic choices as they solve inequalities. Students have the opportunity to construct viable arguments and critique the reasoning of others as they engage in error analysis (MP3).