# Informal Proof of Angle-Angle Criterion

Videos and solutions to help Grade 8 students learn an informal proof of the Angle-Angle (AA) criterion for similar triangles and present informal arguments as to whether or not triangles are similar based on Angle-Angle criterion.

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Lesson Plans and Worksheets for Grade 8

Lesson Plans and Worksheets for all Grades

## New York State Common Core Math Module 3, Grade 8, Lesson 10

### Lesson 10 Student Outcomes

• Students know an informal proof of the Angle-Angle (AA) criterion for similar triangles.
• Students present informal arguments as to whether or not triangles are similar based on Angle-Angle criterion.

### Lesson 10 Summary

• Two triangles are said to be similar if they have two pairs of corresponding angles that are equal.

### NYS Math Module 3 Grade 8 Lesson 10

Classwork
Concept Development
Exercises
1. Use a protractor to draw a pair of triangles with two pairs of equal angles. Then measure the lengths of sides, and verify that the lengths of their corresponding sides are equal in ratio.
2. Draw a new pair of triangles with two pairs of equal angles. Then measure the lengths of sides, and verify that the lengths of their corresponding sides are equal in ratio.
Example 1 - 3
Are the triangles shown below similar? Present an informal argument as to why they are or why they are not.
Exercises 3 - 5
Are the triangles shown below similar? Present an informal argument as to why they are or why they are not.