standard_description: Understand that a function is a rule that assigns to each input exactly one output. The graph of a function is the set of ordered pairs consisting of an input and the corresponding output. (Function notation is not required in Grade 8.)
problem_activity: Activity
This info gap activity gives students an opportunity to determine and request the information needed to find and graph the transformation of a given function. In each case, the given function is a trigonometric function which has been translated horizontally or vertically and also reflected or scaled. The problem card gives the graph and equation of the trigonometric function. The student with the problem card figures out which transformations to apply to the graph and equation. The data cards give multiple ways for students to figure out the transformation. Monitor for students who
ask for the explicit transformations and the order in which they are applied
ask for the amplitude, midline, and period of the new function
The info gap structure requires students to make sense of problems by determining what information is necessary, and then to ask for information they need to solve it. This may take several rounds of discussion if their first requests do not yield the information they need (MP1). It also allows them to refine the language they use and ask increasingly more precise questions until they get the information they need (MP6).
Here is the text of the cards for reference and planning:
[IMG]
Launch
Tell students they will continue to work on identifying transformations between two functions. Explain the info gap structure, and consider demonstrating the protocol if students are unfamiliar with it.
Arrange students in groups of 2. In each group, distribute a problem card to one student and a data card to the other student. After you review their work on the first problem, give them the cards for a second problem and instruct them to switch roles.
Provide students with access to small sheets of graph paper.
Engagement: Develop Effort and Persistence.
Display or provide students with a physical copy of the written directions. Check for understanding by inviting students to rephrase directions in their own words. Keep the display of directions visible throughout the activity.
Supports accessibility for: Memory; Organization
Conversing:
This activity uses
MLR4 Information Gap
to give students a purpose for discussing information necessary to find and graph the transformation of a given function. Display questions or question starters for students who need a starting point such as: “Can you tell me . . . (specific piece of information)”, and “Why do you need to know . . . (that piece of information)?"
Design Principle(s): Cultivate Conversation
Student Facing
Your teacher will give you either a problem card or a data card. Do not show or read your card to your partner.
If your teacher gives you the data card:
Silently read the information on your card.
Ask your partner “What specific information do you need?” and wait for your partner to ask for information. Only give information that is on your card. (Do not figure out anything for your partner!)
Before telling your partner the information, ask “Why do you need to know (that piece of information)?”
Read the problem card, and solve the problem independently.
Share the data card, and discuss your reasoning.
If your teacher gives you the problem card:
Silently read your card and think about what information you need to answer the question.
Ask your partner for the specific information that you need.
Explain to your partner how you are using the information to solve the problem.
When you have enough information, share the problem card with your partner, and solve the problem independently.
Read the data card, and discuss your reasoning.
Student Response
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Student Facing
Are you ready for more?
Suppose we considered the function
\(T\)
which is the sum of
\(Q\)
and
\(S\)
. Is
\(T\)
also periodic? If yes, what is its period? If no, explain why not.
Student Response
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for free access to Extension Student Response.
Activity Synthesis
After students have completed their work, share the correct answers and ask students to discuss the process of solving the problems. Focus on these points:
The order of the transformations matters. For problem card 1, if the vertical stretch is done before the vertical translation it gives a different result, namely
\(Q(x) = 4\sin(2x) + 14\)
. For problem card 2, if the horizontal stretch is done first and then the horizontal translation the result would be
\(S(x) = \text-\cos(\pi (x + \pi))+3\)
For the first card, the vertical translation will take
\(\sin(2x) + 3\)
to
\(\sin(2x )+ 5\)
. For the vertical stretch, make sure students understand that both
\(\sin(2x)\)
and
\(5\)
need to be scaled by 4. The vertical stretch by 4 multiplies the output of the function by 4 and in this case the output, after the translation, is
\(\sin(2x) + 5\)
.
For the second card, the horizontal translation changes
\(\text-\cos(x) + 3\)
to
\(\text-\cos(x+\pi) + 3\)
and then the horizontal scaling by
\(\frac{1}{\pi}\)
gives
\(\text-\cos(\pi x + \pi) + 3\)
. Unlike problem card 1, the scaling does not influence the constant 3 because the scale is horizontal while the 3 translated the graph vertically.
Ask students if they considered asking for the amplitude, period, and midline. In a sense, this information may be more straightforward to process because the order of the transformations is already encoded in this information. But the student with the problem card may not realize that this information is available.
Finally, ask students if they considered sketching the graph first and using this to find the transformed function. The sketch can help show major features of the graph (amplitude, midline, period) and serve as a guide for finding a valid equation.


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