In this activity, students revisit the angles they drew in the preceding lesson and sort them into two groups, based on the features of the angles. While there is no single correct way to sort the angles (as long as the categories are reasonable or can be explained), the goal is to highlight classification of angles by size—as greater than or less than a right angle. Students learn the terms acute angle and obtuse angle in the Activity Synthesis. Consider creating a poster of the graphic organizer from the student book in advance to support the Lesson Synthesis discussion.

When students sort the angles, they look for important features or properties of the angles, including their measure and also, perhaps, looking at the orientation of the rays making the angles (MP7).

This activity uses MLR2 Collect and Display. Advances: conversing, reading, writing.

• Select groups to share their categories, saving the categories that are based on the size of the angle (for example “pointy” and “wide”) to the end.
• “Are there any other words or phrases that are important to include on our display?”
• As students share responses, update the display, by adding (or replacing) language, diagrams, or annotations. Refer to relevant displays from earlier lessons, if possible.
• Remind students to borrow language from the display as needed.
• Introduce acute angle as an angle that is less than and obtuse angle as an angle greater than , and add these words to the vocabulary display from the lesson.
• “Is a angle acute or obtuse?” (Neither. It’s a right angle—a category of its own.)
• “Let’s try to use these words in the next activity as we explain our reasoning.”

In this activity, students classify a angle as a straight angle and further develop their understanding of acute and obtuse angles. Given a pair of intersecting segments, they explain why the figure contains both an acute angle and an obtuse angle.

Some students may wish to measure the angles in the letter Y in the second question. Provide access to protractors if requested.

• Invite students to share responses to the first question.
• Highlight that when two rays that meet at the same point extend out in opposite directions, they form a angle and a straight line.
• Introduce straight angle as an angle that is .
• Select students to share responses to the second question, using the chart from the previous activity as a reference to reinforce acute and obtuse angles.
• Emphasize the idea introduced earlier in the unit—that when two rays share a point, two or more angles are formed.

In this activity, students encounter angles in various forms—in diagrams, descriptions, a construction drawing, and pattern blocks—and practice classifying them by size.

Students should have no trouble distinguishing angles without a protractor, but some students may wish to use a protractor to verify their classification.

The second question prompts students to label the angles in a drawing of a roof structure, which contains many angles. It is not essential that they catch all acute, right, and obtuse angles in the drawing, as long as they identify some of each.

For the last question, provide access to pattern blocks if requested.

• Select students to share their responses to the first question.
• Select other students to share their labeled drawings for the second question, or display the drawing of the roof structure for them to mark up.
• As students share, add images and labels to the chart, with language describing obtuse and acute angles from the first activity.
• Invite students who haven’t shared before to discuss their responses to the last set of questions. Ask them to point to the angles in the pattern blocks to support their responses.
• If students mention only one pattern block, ask: “Are there other shapes Diego could be holding? Which one(s)? How do you know?”