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Lesson Plans and Worksheets for Grade 8
Lesson Plans and Worksheets for all Grades

Examples, videos, and solutions to help Grade 8 students learn to present informal arguments as to whether or not two triangles are similar and how to find lengths of corresponding sides of similar triangles.

Lesson 11 Student Outcomes

• Students present informal arguments as to whether or not two triangles are similar.
• Students practice finding lengths of corresponding sides of similar triangles.

Lesson 11 Summary

• Given just one pair of corresponding angles of a triangle as equal, use the side lengths along the given angle to determine if triangles are in fact similar.
• Given similar triangles, use the fact that ratios of corresponding sides are equal to find any missing measurements.

NYS Math Module 3 Grade 8 Lesson 11

Classwork
Example 1 & 2
Given the information provided, is △ ABC ∼ △ DEF?

Example 3
Given that △ ABC ∼ △ AB'C', could we determine the length of AB'?

Example 4
If we suppose XY is parallel to X'Y', can we use the information provided to determine if △ OXY ∼ △ OX'Y'?
Explain.

Example 5
Given the information provided, is △ OPQ ∼ △ Op'Q'?

Exercises
1. In the diagram below, you have △ ABC and △ AB'C'.
Use this information to answer parts (a)–(d).
a. Based on the information given, is △ ABC ∼ △ AB'C'? Explain.
b. Assume line BC is parallel to line B'C'. With this information, can you say that △ ABC ∼ △ AB'C'. Explain.
c. Given that △ ABC ∼ △ AB'C' determine the length of AC'.
d. Given that △ ABC ∼ △ AB'C' determine the length of AB.

2. In the diagram below, you have △ ABC and △ A'B'C'.
Use this information to answer parts (a)–(c).
a. Based on the information given, is △ ABC ∼ △ A'B'C'? Explain.
b. Given that △ ABC ∼ △ A'B'C' determine the length of A'C'.
d. Given that △ ABC ∼ △ A'B'C' determine the length of BC.

3. In the diagram below, you have △ ABC and △ A'B'C'. Use this information to answer the question below. Based on the information given, is △ ABC ∼ △ A'B'C'?
Explain.

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