Lesson objective: Understand that slicing a three-dimensional figure creates a new two-dimensional face.

Students bring prior knowledge of using nets to represent three-dimensional figures from CCSS 6.G.A.4. This prior knowledge is extended to three-dimensional figures that are sliced into two smaller figures as students identify the two-dimensional shape of the new face. A conceptual challenge students may encounter is visualizing a three dimensional figure from a two-dimensional image.

The concept is developed through work with a model pyramid, which shows that the shape of the new face of a sliced figure, is dependent on the shape of the original figure as well as where it is sliced.

This work helps students deepen their understanding of equivalence because the shape of a three-dimensional figure determines the shape of the new faces created when the figure is sliced.

Students engage in Mathematical Practice 4 (model with mathematics) as they apply their undersatnding of three-dimensional figures to identify the shape of the new face.

**Key vocabulary:**

- face
- three-dimensional figure
- two-dimensional figure
- slice