This Instructional Activity is a part of the Lesson 10, Unit 3, Grade 8. Did everyone notice that they had similar triangles in Exercises 1 and 2? If students respond no, ask them how close the ratios were with respect to being equal. In some cases, human error either in measuring the angles or side lengths can cause the discrepancy. Another way around this is by selecting ahead of time one student to share her work on a document camera for all to see. To develop conceptual understanding, students may continue to generate triangles with two pairs of equal angles and then generalize to develop the AA criterion for similarity.