# Lesson Plan: Slope and Similar Triangles

## Lesson Objectives

• Connect slope to similar triangles
• Use similar triangles to find slope
• Understand slope's geometric interpretation

## TEKS Standards

• 8.4B: Graph proportional relationships, interpreting unit rate as slope.
• 8.4C: Use data to determine rate of change or slope and y-intercept.
• 8.3A: Understand ratio of corresponding sides in similar shapes.
• 8.3B: Compare attributes of a shape and its dilation on coordinate plane.

## Key Vocabulary and Concepts (15 min)

### Concept Development

Show the following video, which shows how similar right triangles can be used to explore slope:

## Review (10 min)

• Use these clip art images to see if students can determine if the two right triangles are similar.

https://www.media4math.com/library/75380/asset-preview

•  For each of the lines shown, have students calculate the slope. Have them use the underlying grid to make their calculations. Then have them compare the slopes.

https://www.media4math.com/library/75381/asset-preview

## Assessment (10 min)

Use this assessment to check for student understanding.

## Quiz

1. What is the slope of a line?

2. If two triangles have the same shape but different sizes, what are they called?

3. How can you determine if two triangles are similar?

4. What is the relationship between the slopes of the hypotenuses of similar right triangles?

5. If one side of a triangle is doubled and the other sides are left unchanged, what happens to the slopes of the sides of the new triangle compared to the original triangle?