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# Course 3, Unit 3 - Similarity and Congruence

Overview
In this unit, students develop understanding and skill in the use of similarity and congruence relations to solve problems involving shape and size. In each of the two lessons, students have many opportunities to continue to develop skill and confidence in reasoning deductively using both synthetic and coordinate methods.

Key Ideas from Course 3, Unit 3

• Similarity: Conditions for polygons to be similar with special attention to triangles and parallelograms are developed.

• Congruence: Conditions for polygons to be congruent with special attention to triangles and parallelograms are developed.

• Centers of triangles: The three centers of triangles studied in this unit are those formed by the perpendicular bisectors of the sides, the angle bisectors, and the medians. (See pages 200-203.)

• Congruence-preserving transformations: The properties of transformations and composites of transformations are re-examined in this unit. These transformations were introduced in the coordinate setting in Course 3 Unit 3, Coordinate Methods.