Overview:  The teacher attempts to correct the false logic that some students may have used to solve the problem (as in Explore 8).  Specifically, students should have selected three points and then located a new point equidistant from those three points.  Instead, some students first selected a point for the new grocery store, and then they identified three points approximately around that new point.  The teacher points out for students that their logic has gone in the wrong direction.  The three points should have been students’ givens, from which they could locate a new point.

Prior knowledge:  The teacher connects with the mathematical practice of applying a particular order of logic to solve a problem.  The teacher reminds students that one of the important things they learn in geometry is the practice of applying deductive reasoning.

Other points of interest:  The teacher makes an analogy between the givens of the grocery store problem and the logic of an “if-then” statement.  In addition, the teacher attempts to make an analogy with the arguments students make in everyday life, apart from geometry.