In this lesson, students use tactile tools to find angle measurements and observe more clearly that angles are additive. They compose and decompose angles by arranging paper cutouts, by folding paper or tracing, and by drawing diagrams. Students arrange smaller angles, the sizes of which are unknown, into larger angles with familiar sizes and features (, , and ). Once the measurement of an angle is known, they use it to find those of other angles. For example, if two copies of Angle X form a right angle, Angle X must be . If another angle, Z, can be decomposed into three of these angles, then Z must be .

Encourage students to continue to collect, define, and illustrate new terms to support communication and reasoning at the end of each lesson.