standard_description: Construct a function to model a linear relationship between two quantities. Determine the rate of change and initial value of the function from a description of a relationship or from two (x, y) values, including reading these from a table or from a graph. Interpret the rate of change and initial value of a linear function in terms of the situation it models, and in terms of its graph or a table of values.
problem_activity: Activity
In this activity, students choose a graphing window to tell a particular story.
Launch
Continue access to graphing technology. Students may be ready to dive into the activity without much assistance, or may need to engage in a notice and wonder to familiarize themselves with the context and the information encoded in the equation and the graph.
Student Facing
Suppose
\(y=0.50d + 4\)
represents the cost of renting a car,
\(y\)
, as a function of miles driven,
\(d\)
. Here’s a graph representing the function.
[IMG]
What is the graphing window used for the given graph?
Find a graphing window so that:
It gives the impression that the charge per mile driven is very high and the total rental cost gets really expensive really fast.
It gives the impression that the charge for every mile driven is close to nothing and the total rental cost will be pretty low even if the car is driven many miles.
Student Response
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Activity Synthesis
Invite selected students to share their responses. Questions for discussion:
“What adjustments to the graphing window make the cost seem lower? What adjustments make the cost seem higher?” (The graph in the second question make the cost seem lower, because the graph looks quite flat and close to the horizontal axis. The graph is the first question make the cost seem higher, because the graph looks quite steep.)
“For each situation, how did you decide whether to make the graph look flatter or steeper?” (I thought about whether the situation suggested the function should be increasing slowly or quickly.)
“What were some strategies to make the graph look flatter?” (Keep the domain the same or smaller, and make the range larger.)
“What were some strategies to make the graph look steeper?” (Keep the range the same, and make the domain larger.)
“In most graphing technology, you can zoom in or zoom out. Why might you want to set a specific graphing window, instead of zooming in or out?” (Zooming in or out often doesn’t change the overall shape of the graph, because the domain and range are being scaled by the same amount. Choosing a specific graphing window allows you more control over what is shown.)


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