This lesson invites the question, “How much information is needed to guarantee that two triangles are congruent?” Students start to answer this question in an Information Gap. When students request information about sides and angles, students must attend to precision (MP6). In an optional activity, students study character dialogues from the Information Gap to highlight the ambiguity of requesting two sides and an angle.

Throughout this lesson, students are developing and testing conjectures about how much information they need to prove triangles are congruent (MP8). They will then write these proofs over the next several lessons. The process of experiment, conjecture, test, and adjust or prove is the essence of doing mathematics.

Technology isn’t required for this lesson, but there are opportunities for students to choose to use appropriate technology to solve problems. We recommend making technology available.