Lesson objective: Understand that angles are geometric figures.

Students bring prior knowledge of polygons from 2.G.A.1. This prior knowledge is extended as, in the process of composing and decomposing shapes, students consider geometric building blocks such as angles. A conceptual challenge students may encounter is combining rays to create a new geometric figure, an angle. Teachers who observe that their students bring strong knowledge of 2.G.A.1 may decide to skip this lesson or condense it into a shorter lesson.

The concepts in this lesson are developed through work with models of rays, which can be arranged in different ways to compose new geometric figures.

This work helps students deepen their understanding of number because the number of geometric building blocks used to create a figure can help to define it.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they consider different arrangements of rays as they construct a model of a hexagon.

**Key vocabulary:**

- angle
- attribute
- closed
- endpoint
- figure
- polygon
- quadrilateral
- ray
- vertex