Geometry Module 2, Topic A, Lesson 5

Student in Library

In the last lesson, students learned about the triangle side splitter theorem, which is now used to prove the dilation theorem.  In Grade 8 students learned about the fundamental theorem of similarity (FTS), which contains the concepts that are in the dilation theorem presented in this lesson.  We call it the dilation theorem at this point in the module because students have not yet entered into the formal study of similarity.  Some students may recall FTS from Grade 8 as they enter into the discussion following the Opening Exercise.  Their prior knowledge of this topic will strengthen as they prove the dilation theorem.

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Common Core Learning Standards

CCLS State Standard
G.SRT.1.a A dilation takes a line not passing through the center of the dilation to a parallel line, and...
G.SRT.4 Prove theorems about triangles. Theorems include: a line parallel to one side of a triangle divides...

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