This lesson is about properties of quadrilaterals and learning to investigate, formulate, conjecture, justify, and ultimately prove mathematical theorems. The idea for the lesson came from two sources:

The "Shape of Things" Problem of the Month and its related Teacher Notes

The John Van de Walle mathematics series’ investigation of the diagonals of a quadrilateral

Taught by: Cathy Humphreys, Fremont High School, Fremont Union High School District, Sunnyvale, California

Mathematical Strand:

- Geometry: Congruence

- The Shape of Things Problem of the Month Packet PDF
- Describing the Ideal Classroom, which reviews this video lesson in the Appendix PDF
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