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Unit 2 - Lesson 9 - Grade 8: Illustrative Mathematics

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Grade 8 Unit 2
Lesson 9: Side Length Quotients in Similar Triangles
CC BY 2021 Illustrative Mathematics®
Grade 8 Unit 2
Lesson 9: Side Length Quotients in Similar Triangles
CC BY 2021 Illustrative Mathematics®
Lesson: Side Length Quotients in Similar Triangles

Two-three-four and Four-five-six (Warm Up)

1.

Triangle A has side lengths 2, 3, and 4. Triangle B has side lengths 4, 5, and 6. Is Triangle A similar to Triangle B?

Quotients of Sides Within Similar Triangles

Triangle ABC is similar to triangles DEF, GHI, and JKL. The scale factors for the dilations that show triangle ABC is similar to each triangle are in the table.
2.

Find the side lengths of triangles DEF, GHI, and JKL. Record them in the table.

3.

Your teacher will assign you one of the three columns. For all four triangles, find the quotient of the triangle side lengths assigned to you and record it in the table.

4.

Compare your results with your partners’ and complete your table.

Using Side Quotients to Find Side Lengths of Similar Triangles

5.

Triangles ABC, EFD, and GHI are all similar. The side lengths of the triangles all have the same units. Find the unknown side lengths.


Cool Down: Similar Sides

Similar Sides

6.

The two triangles shown are similar. Find the value of a/b.