Lesson Plan: The Slope Formula

Lesson Objectives

• Learn and apply the slope formula
• Calculate slope given two points
• Use slope formula in various contexts

TEKS Standards

• 8.4C: Use data to determine rate of change or slope and y-intercept.
• 8.5I: Write linear equations using various representations.
• A.3B: Calculate rate of change of linear functions.
• A.3C: Graph linear functions and identify key features.

Prerequisite Skills

• Understanding the concept of slope
• Identifying different types of slopes (positive, negative, zero, undefined)
• Visualizing slope on a graph (https://www.media4math.com/LessonPlans/VisualizingSlopeOnGraph)
• Recognizing similar triangles and their properties (https://www.media4math.com/LessonPlans/SlopeSimilarTriangles)

1. Warm-up (5 minutes)

Review the previous lesson on types of slopes (https://www.media4math.com/LessonPlans/TypesOfSlope). Ask students to identify the slope of various line segments shown on the board or projector. Make the following observations:

• Previous ways of calculating slope were more geometric and visual (coordinate grids, measuring the rise and run).
• What if the only information you have about two points are their coordinates? How could you calculate the slope?

2. Teach (15 minutes)

Show students the definition of the slope formula: https://www.media4math.com/library/22185/asset-preview

Elaborate on the following points:

• The slope formula provides an algebraic way of calculating slope.
• The algebraic symbol for slope is m.
• The slope formula uses the coordinates of the two points to calculate the slope.
• The slope formula is the ratio of the change in the y-coordinates (the rise) to the change in the x-coordinates (the run)

Relate this to the concept of slope as the rise over the run (https://www.media4math.com/LessonPlans/WhatIsSlope).

Engage

Explain why someone would use the slope formula:

• To precisely calculate the slope between any two points on a line
• To determine if two lines are parallel (same slope) or perpendicular (negative reciprocal slopes)
• To write the equation of a line when given two points it passes through

Explore

Show students the following math examples using the slope formula:

• Example 1 (positive slope): https://www.media4math.com/library/25039/asset-preview
• Example 2 (negative slope): https://www.media4math.com/library/25040/asset-preview
• Example 3 (zero slope): https://www.media4math.com/library/25041/asset-preview

Additional examples can be found here: https://www.media4math.com/MathExamplesCollection--SlopeFormula to guide students through solving examples using the slope formula. Project or distribute the step-by-step examples, and have students follow along as you solve them together. 

You can also show the following video tutorials using the slope formula, which go through a step-by-step process for using the slope formula:

• Example 1 (zero slope): https://www.media4math.com/library/74283/asset-preview
• Example 2 (positive slope): https://www.media4math.com/library/74284/asset-preview
• Example 3 ( negative slope): https://www.media4math.com/library/74286/asset-preview

 Explain

Break down the slope formula and discuss how to plug in coordinates to find the slope. Emphasize the importance of the order of the points and how it affects the sign of the slope.

3. Review (5 minutes)

Review slope and the slope formula with this presentation: https://www.media4math.com/library/21537/asset-preview.

4. Assess (10 minutes)

Distribute a 10-question quiz where students find the slope between various pairs of points. Include questions that cover positive, negative, zero, and undefined slopes. This assessment will help you evaluate their understanding of the slope formula and their ability to apply it correctly.

Quiz

1. Find the slope of the line passing through the points (2, 3) and (5, 7).
   
    
2. Calculate the slope of the line passing through the points (-4, 2) and (3, -5).
   
    
3. Determine the slope of the line passing through the points (0, 0) and (6, 0).
   
    
4. Find the slope of the line passing through the points (1, 4) and (1, -2).
   
    
5. Calculate the slope of the line passing through the points (-2, 5) and (4, 5).
   
    
6. Determine the slope of the line passing through the points (3, -1) and (3, 4).
   
    
7. Find the slope of the line passing through the points (0, 0) and (0, 0).
   
    
8. Calculate the slope of the line passing through the points (2, -3) and (-1, 4).
   
    
9. Determine the slope of the line passing through the points (5, 2) and (-3, -4).
   
    
10. Find the slope of the line passing through the points (4, 0) and (0, 3).

Answer Key

1. 1 1/3
   
    
2. -1
   
    
3. 0
   
    
4. Undefined
   
    
5. 0
   
    
6. Undefined
   
    
7. Undefined.
   
    
8. -2 1/3
   
    
9. 0.75
    
10. -0.75

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