Illustrative Mathematics
What is a Trapezoid? (Part 2)
This collaborative activity investigates the meaning of a trapezoid and a parallelogram. It begins by presenting two different definitions of a trapezoid. Learners are to reason abstractly the difference between the two definitions and...
Curated OER
Symmetry and Geometric Shapes on Campus
Build on your learners' previous knowledge of geometric shapes and symmetrical figures. Then set them out to take photos of geometric shapes on campus. They assess whether the photos contain symmetry or not.
National Council of Teachers of Mathematics
The Math Forum: Defining Geometric Figures
This site provides an in-depth definition of a two-dimensional figure and a three-dimensional figure. Related terms include arcs, vertices, polygon, and many more.