# Lesson 2:

Similar Triangles (Similarity Postulates, Proportionality Theorem, and Midsegment Theorem)

## Clarifying the Learning

### Lesson Overview

In this lesson you will discover the properties of similar triangles and determine if two triangles are similar. In the last lesson, we looked at similar figures. We discovered that in order for two figures to be similar, their angles have to be congruent. In this lesson, we are going to focus on triangles. An important question that we will explore is whether or not we need to know that all three angles of triangle are congruent to three angles of a second triangle in order to guarantee that the triangles are similar. If we do not have information on all three angles in two triangles, are their other ways that we can prove the triangles similar? We will also look at the Proportionality and Midsegment Theorems in triangles.

### Driving Question

What methods/postulates can I use to prove that two triangles are similar?

## Defining Success

### Content Standards and Objectives:

After completing this lesson, you should be able to use the properties of similarity transformations to establish the AA criterion for two triangles to be similar.**(M.2HS.STP.3)(CCSS.Math.Content.HSG-SRT.A.3)**

Upon mastering this objective, you should be able to conduct the tasks in the video below:

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You should also be able to use congruence and similarity criteria for triangles to solve problems and to prove relationships in geometric figures..**(M.2HS.STP.8)(CCSS.Math.Content.HSG-SRT.B.5)**

Upon mastering this objective, you should be able to conduct the tasks in the video below:

If you have trouble viewing this video, click here to download.