Unit 48: Similarity and Congruence

Day 28 of 30

Dilations and similarity

9-10Mathematics

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Learning Objective

Students will explore dilations and similarity through guided practice and application.

Today's Lesson

This lesson focuses on dilations and similarity. Mathematics provides tools for modeling and analyzing complex systems.

Similar figures have the same shape but not necessarily the same size—corresponding angles are equal and corresponding sides are proportional. Scale factor k: ratio of corresponding lengths. For triangles: AA (two angles), SSS (sides proportional), SAS (two sides and included angle proportional). Similarity is used for indirect measurement, scale drawings, and proofs!

As you engage with this material, consider both the theoretical foundations and practical applications. Think critically about how this concept builds on prior knowledge and where you might apply it beyond the classroom.

Challenge yourself to go beyond memorization—seek to understand the "why" behind the processes and principles.

Key Terms
Problem

A mathematical question requiring analysis and solution

Solution

The result obtained by solving a problem

Activities
Instructions
1. Review the example problems for dilations and similarity. 2. Identify the steps and strategies used. 3. Work through practice problems independently. 4. Compare solutions with a partner.
Materials Needed
  • Notebook
  • Calculator (if needed)
  • Graph paper
Practice Problems
1

Two similar triangles have scale factor 3. If a side in the smaller is 4, find the corresponding side in the larger.

Hint: Multiply by scale factor.
2

Similar figures: scale factor 2. How does area change?

Hint: Area scales by k².
3

Scale factor 1/2. If a length in the original is 10, what is it in the image?

Hint: Multiply by 1/2.

Teaching Tip

For advanced learners: Encourage deeper analysis and real-world connections. Consider extension activities that allow students to apply dilations and similarity to novel situations.

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