In this lesson, students combine their ability to find unknown angles and use angles to make conclusions about the relative lengths of sides in a figure made up of several triangles. First students look for and make use of structure (MP7) to find unknown angles in images made up of one to three. This activity reviews complementary and supplementary angles, vertical angles, and properties of special triangles. Then students revisit the idea that larger angles are opposite longer sides while critiquing some incorrect and incomplete reasoning (MP3). Finally, students put these ideas together for a figure made up of more than three triangles.

Math Community
In this lesson, students review the themes that arose when they shared their initial thoughts in Exercise 1 about what they think it should look like and sound like to do math together as a community. Students then have a chance to both affirm and add to the ideas that were generated.