This Instructional Activity is a part of the Lesson 7, Unit 3, Grade 8. Begin by asking students to brainstorm what they already know about dilations. Accept any reasonable responses. Responses should include the basic properties of dilations;for example,lines map to lines, segments to segments, and rays to rays. Students should also mention that dilations are angle-preserving. Let students know that in this lesson they informally prove why the properties are true.