An informal proof of the Angle-Angle (AA) criterion for similar triangles and informal arguments as to whether or not triangles are similar based on Angle-Angle criterion, with video lessons, examples and step-by-step solutions for students in Grade 8 and also for SAT/ACT prep.

**Related Pages**

Similar Triangles

Lesson Plans and Worksheets for Grade 8

Lesson Plans and Worksheets for all Grades

More Lessons for Grade 8

Common Core For Grade 8

Download Worksheets for Grade 8, Module 3, Lesson 10

- 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.

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

**Concept Development**

**Exercises**

- 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.
- 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.

**Examples 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.

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