standard_description: Interpret the equation y = mx + b as defining a linear function, whose graph is a straight line; give examples of functions that are not linear. For example, the function A = s2 giving the area of a square as a function of its side length is not linear because its graph contains the points (1,1), (2,4) and (3,9), which are not on a straight line.
problem_activity: Optional activity
Students interpret the slope and intercepts in the context of the situation. They also discuss limitations of the mathematical model.
This activity can be extended by having students investigate if temperature on other continents or across continents fits the same pattern that we found for North America.
Launch
Keep students in same groups of 3–4.
Student Facing
Refer to your equation for the line that models the association between latitude and temperature of the cities.
What does the slope mean in the context of this situation?
Find the vertical and horizontal intercepts and interpret them in the context of the situation.
Can you think of a city or a location that could not be represented using this same model? Explain your thinking.
Student Response
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Anticipated Misconceptions
Students may want to say “For every one unit increase in
\(x\)
,
\(y\)
decreases by 1.07 units.” Ask them to use the specific units and quantities in the model, latitude in degrees north and temperature in degrees Fahrenheit.
Activity Synthesis
Invite students to share their responses. Discuss the limitations and uses of the model. Consider asking the following questions:
“What are some limitations of the model?”
“Do limitations mean that the model is not good?” (No, it just means that we have to be aware of when we can use it and when we can’t use it. Our model is pretty good for latitudes between 25 and 65 degrees north, and for locations in North America.)
“What questions do you have about predicting temperature?”
“How could you extend your investigation of predicting temperature or the weather?”
Engagement: Develop Effort and Persistence.
Break the class into small discussion groups and then invite a representative from each group to report back to the whole class.
Supports accessibility for: Language; Social-emotional skills; Attention


aligns: no