In a previous lesson, students justified that, if all pairs of corresponding sides and angles are congruent, then the two triangles must be congruent. 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 Info Gap. When students request information about sides and angles, students must attend to precision (MP6). In subsequent activities, students study character dialogues from the Info Gap to highlight the ambiguity of requesting two sides and an angle or three angles.
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.
Lesson overview
 4.1 Warmup: Make That Triangle (5 minutes)

4.2 Activity: Info Gap: Too Much Information (20 minutes)
 Includes "Are you Ready for More?" extension problem
 4.3 Activity: Too Little Information? (10 minutes)
 Lesson Synthesis
 4.4 Cooldown: Angles All the Way (5 minutes)
Learning goals:
 Generate (orally) conjectures about sufficient conditions to prove that triangles are congruent.
Learning goals (student facing):
 Let’s figure out if there are shortcuts for being sure two triangles are congruent.
Learning targets (student facing):
 I can write conjectures about what I need to know to prove two triangles are congruent.
Required materials:
 Dried linguine pasta
 Geometry toolkits
 Highlighters
 Preprinted slips, cut from copies of the blackline master
 Protractors
 Rulers
Required preparation:
 Create a display labeled “Triangle Congruence Criteria Conjectures” for the lesson synthesis.
Standards:
 This lesson builds on the standards: CCSS.HSGCO.B.7MS.GCO.7MO.G.CO.B.6
 This lesson builds towards the standards: CCSS.HSGCO.B.8MS.GCO.8CCSS.HSGCO.C.10MS.GCO.10CCSS.HSGCO.C.11MS.GCO.11CCSS.HSGSRT.A.3MS.GSRT.3MO.G.CO.B.7MO.G.CO.C.9MO.G.CO.C.10MO.G.SRT.A.3
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