Although the problem begins with a lot of procedural work, drawing triangles, measuring angles, etc., it also leads well to a need for a conjecture, or what Sonia calls an "argument," that angle C is always 90 degrees. By asking the students to measure at least 5 triangles, the teacher has also provided a way to get enough data for students to observe patterns, see discrepancies and make conjectures about both. However, they can begin to see that individual observations, no matter how numerous, will not constitute proof that angle C must be a right angle.

Ms. Saleh's questions bring out that the students understand that something that is true must be true for "every single" case and they see that this is not feasible. It's unclear whether they understand that it could be proved without testing each case, but they are reasoning about the mathematical situation and will move on to testing conjectures.