Big Idea:Often the truest solution to a problem is that "it depends". Substitution is an efficient method for finding the precise intersection of two lines; a graph makes it clear what happens on either side of that point.
Big Idea:The purpose of this lesson is for students to understand how to analyze a system of equations to determine when a plan is cheaper, more expensive, or cost the same at certain points on the graph.
Big Idea:It’s amazing to get to the point where students truly understand how useful and beautiful algebra can be. Transitioning from graphing systems to solving by substitution is an opportunity to get kids there.