Unit 2, Lesson 3
Congruent Triangles, Part 1
Integrated Math 1
Preparation
Lesson Narrative
This lesson introduces students to proofs of triangle congruence by applying point-by-point transformations. They grapple with the idea that the right set of transformations will work for any set of triangles with the right congruent corresponding parts, regardless of position and orientation.
Writing proofs using transformations requires constructing arguments for why the sequence of moves is guaranteed to line up the vertices and sides exactly (MP3). Students practice making their own arguments and then are provided with sentence frames to use in future proofs. A template is provided with the blackline masters for this lesson.
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.
- Justify (orally and in writing) that two triangles are congruent if and only if all corresponding sides and angles are congruent.