options: Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.

Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.
problem_activity: Activity
This activity prompts students to again compare a linear function with an exponential one, but this time without a context, and the exponential function grows much more slowly over a long period of time. Even if students predict that the exponential function will grow more quickly because it is exponential, they still need to decide which one reaches 2,000 first. To do that, students may try:
continuing the table of values with increasingly larger values
using graphing technology
finding when
\(f(x) = 2,\!000\)
and substituting this value (
\(x=1,\!000\)
) into
\(g(x)\)
Making graphing and spreadsheet technology available gives students an opportunity to choose appropriate tools strategically (MP5).
Launch
Present the two equations that define two functions
\(f\)
and
\(g\)
:
\(f(x) = 2x\)
and
\(g(x) = (1.01)^x\)
. Give students a moment to share what they notice and wonder about the functions. Ask questions such as:
What is happening in the first function? What about in the second function?
Which function do you think will reach a value of 2,000 first?
Representing, Conversing: MLR7 Compare and Connect.
Ask students to prepare a visual display that shows their mathematical thinking in response to the question “Which function do you think will reach a value of 2,000 first?” Invite previously identified students to share their representations. In groups of 2, ask students to compare their strategies and discuss how the strategies are the same or different. Consider using the prompt “Which strategy do you believe is the most efficient in determining a solution?” Listen for and amplify observations of advantages and disadvantages to different approaches, such as using a particular approach for a certain time interval. This will help students connect different approaches and determine the effectiveness of each one through partner and whole-class discussion.
Design Principle(s): Cultivate conversation; Maximize meta-awareness
Action and Expression: Provide Access for Physical Action.
Provide access to tools and assistive technologies, such as a graphing calculator or graphing software. Some students may benefit from a checklist or list of steps to be able to use the calculator or software.
Supports accessibility for: Organization; Conceptual processing; Attention
Student Facing
Complete the table of values for the functions
\(f\)
and
\(g\)
.
| \(x\) | \(f(x)\) | \(g(x)\) |
|-------|----------|----------|
|   1   |          |          |
|  10   |          |          |
|  50   |          |          |
|  100  |          |          |
|  500  |          |          |
|       |          |          |
|       |          |          |
|       |          |          |
Based on the table of values, which function do you think grows faster? Explain your reasoning.
Which function do you think will reach a value of 2,000 first? Show your reasoning. If you get stuck, consider increasing
\(x\)
by 100 a few times and record the function values in the table.
Student Response
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for free access to Student Response.
Student Facing
Are you ready for more?
Consider the functions
\(g(x)=x^5\)
and
\(f(x)=5^x\)
. While it is true that
\(f(7)>g(7)\)
, for example, it is hard to check this using mental math. Find a value of
\(x\)
for which properties of exponents allow you to conclude that
\(f(x)>g(x)\)
without a calculator.
Student Response
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click here to register or sign in
for free access to Extension Student Response.
Activity Synthesis
Select students who used contrasting approaches to share. The exponential function
\(g\)
grows sufficiently slowly that it looks like it will not catch up with or ever overtake the linear function
\(f\)
. This is true for a table of values as well as using a graph. Invite students who used contrasting methods to share, in the order shown in the Activity Narrative.
Emphasize that the table needs to be continued for a long time to identify when the values of
\(g\)
become greater than those of
\(f\)
. Similarly, the window of the graph needs to be chosen carefully. A very efficient method is to identify that
\(f(1,\!000)=2,\!000\)
and then evaluate
\(g(1,\!000)\)
. Since
\(g(1,\!000)\)
is much greater than 2,000,
\(g\)
reaches 2,000 first.
If not already illustrated by students who used graphing, show this dynamic sketch and zoom out:
Though for quite a while it doesn't seem like the values of
\(g\)
would ever catch up with those of
\(f\)
, if the growth is allowed to take place long enough, exponential eventually surpasses linear.


correct_option_index: 5