## Graphing Linear Function Using Slope-Intercept – Steps

### This document walks students through the steps for plotting the y-intercept and then using run and rise to plot additional points to draw a line.

The handout starts with a review of prerequisite skills of identify slope and intercept in the equation.

Below are slides from a Google Slides version.

## Matching Activity for Linear Function Representations

Here is a matching activity on a Google Slides file for various representations of a set of linear functions: verbal, symbolic (equation), graphical, and tabular (or data). The students use gallery view of the slides and sort them by function. Then they can change the background color with a different color for each function. This invokes their analytical skills to decipher key elements of the function and of each representation, for example they may identify the value of the y-intercept in the equation and find a graph with the same value.

## Proportional Relationship (with k) vs Linear Function (with m)

There have been interesting discussions on various Facebook Teacher pages about proportional relationships vs linear functions. This mirrors discussion about the constant of proportionality vs slope vs unit rates.

The difference between the proportional relationships and slope is context and the ratios. The ratio for the former addresses the variables themselves. The ratio for the slope addresses the change in the variables. This arises from context. To flesh this out let’s use the pay as a function of hours, with \$15 an hour for the hourly rate.

• If we focus on the fact that to compute the total pay, we multiply by the hours worked by 15 we have a proportional relationship and the \$15 an hour is a constant of proportionality.
• If we focus on the fact that every increase of 1 hour results in an increase of \$15 in our total pay, we have a linear function and the \$15 an hour is a rate of change (or slope of the line). Because of the context, we have different constants (k vs m).

## Group Model for Proportional Relationships and Slope Application

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In my experience, many students struggle with translating word problems modeled by a proportional relationship or a linear function into a algebraic expression or equation. (Image below.)

Here is a link to a Jamboard that can be used to introduce the algebraic expression to model the unit rate. (See image below on how to copy and edit.)

Here is how you can use this to introduce modeling the word problem.

• Start with the unit rate concept. In this case there is \$45 “in” every hour. This is modeled in slide 1 (top 2 photos).
• The next 2 photos show slide 2 in which the student duplicates the \$45 image and fills 2 hours, with \$45 “in” each. They complete the multiplication expression by multiplying by 2.
• This is followed by the same steps for 3 hours (photo bottom left) and sequentially to 6 hours.
• In the last slide there are no hours shown because the # of hours is unknown. This leads to using “X” to represent the unknown NUMBER of hours (I don’t let students get away with x=hours) and finally the algebraic expression (bottom photo).

You can make a copy and edit it.