# Dueling Methods for Writing the Equation of a Line

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## Objective

SWBAT write the equation of a line using the slope-intercept form and point-slope form.

#### Big Idea

The purpose of this lesson is to introduce the students to point-slope form by using a comparison chart with slope-intercept form.

## Warm up

10 minutes

Today's Warm up is intended for the students to complete in 5 minutes.  It sets up the introduction of a new model for linear functions. I have not introduced the point-slope form to write the equation of a line previously. Therefore, I instruct my students to complete only the left side of the comparison chart.  In other words, I expect my students to write the equation of a line using slope-intercept form, y=mx + b.

After my students complete the Warm Up, I will demonstrate point-slope form by completing the right side of the comparison chart. I encourage my students to take notes as they follow along and complete the right side of the table with me. I demonstrate introducing the Warm Up and using Point-Slope form in the following video:

## Independent Practice

15 minutes

I want to give my students a lot of time for practice today, so I will allow them to work on the Independent Practice until there are about 10 minutes left in the period. The Independent Practice is similar to the Warm-up: students to write the equation of a line using slope-intercept form on one side of the worksheet. On the other side, they use point-slope form.

Because I want students to recognize linear relationships in different forms, in this practice students to write the equations of the lines from different representations:

• a linear graph
• a point and a slope
• two points
• an x-intercept and a slope
• two points with the same x value
• a table

At the end of the Independent Practice I provide a Select All type multiple choice question. Students will be assessed in this format on the PARCC Exam this year.

With about 10 minutes left in the period, I instruct the students to complete the Independent Practice as homework to be handed in the next day and we move on to today's Exit Slip.

## Exit Slip

10 minutes

Today's Exit Slip requires about 10 minutes.  It provides me with a quick formative assessment to check student understanding of using Point-Slope Form to write the equation of a line. The students are instructed to use Point-Slope Form, but I expect some students will apply Slope-Intercept Form.

Examples of Student Work

• Student 1 solved the equation correctly for the y intercept, but then wrote y=3x -17.
• Student 2 calculated the wrong slope and then distributed incorrectly to the 2nd term in the parentheses.
• Student 3 wrote the correct equation y=3x + 17

Based on the examples shown here, I learned that it will be important to emphasize precision (MP6) in future lessons because many errors were small and resulted from a lack of precision in the application of a method.