Explain triangle congruence criteria

Start lessonBegins with Triangle congruence criteria proofs · Slides

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Lesson Plan →Objectives, pacing and practice, built from this lesson's brief.
Guided Notes →One page your students fill in and keep.
Exit Ticket →Three items at the end of class. No student accounts.
Re-teach →After an exit ticket: who missed what, and what to do tomorrow.
Homework →Assign practice; it grades itself.

HSG.CO.B.8

**HSG.CO.B.8**: Explain how the criteria for triangle congruence (ASA, SAS, and SSS) follow from the definition of congruence in terms of rigid motions.

HSG.CO.B.8: Explain how the criteria for triangle congruence (ASA, SAS, and SSS) follow from the definition of congruence in terms of rigid motions.

What you'll learn

Explain why the SAS criterion (two sides and the included angle) is sufficient to guarantee triangle congruence, using the rigid-motion construction from CO.B.7
Explain why the ASA criterion (two angles and the included side) is sufficient to guarantee triangle congruence, using rigid motions and the triangle angle sum property
Explain why the SSS criterion (three sides) is sufficient to guarantee triangle congruence, using rigid motions and the properties of circle intersections
Explain why certain combinations of parts -- specifically SSA (two sides and a non-included angle) and AAA (three angles) -- do NOT guarantee congruence, by constructing explicit counterexamples
Use SAS, ASA, and SSS as efficient shortcuts for establishing triangle congruence in geometric proofs, replacing the need to verify all six pairs of corresponding parts

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