This Problem Set is a part of the Lesson 7, Unit 3, Grade 8. In this lesson, students think about the mathematics behind why those statements are true in terms of an informal proof developed through a discussion. Responses should include the basic properties of dilations; for example, lines map to lines, segments to segments, and rays to rays.Students know an informal proof of why dilations are angle-preserving transformations. Students know an informal proof of why dilations map segments to segments, lines to lines, and rays to rays.