Exponential Modeling and Logarithms

Lesson 7

Math

Unit 5

11th Grade

Lesson 7 of 16

Objective


Describe and evaluate simple numeric logarithms (Part I).

Common Core Standards


Core Standards

  • F.LE.A.4 — For exponential models, express as a logarithm the solution to abct = d where a, c, and d are numbers and the base b is 2, 10, or e; evaluate the logarithm using technology.

Foundational Standards

  • N.RN.A.1
  • N.RN.A.2

Criteria for Success


  1. Describe the pattern in converting between logarithms and exponential equations and describe the purpose of logs.
  2. Write logs as exponents and exponents as logs.
  3. Evaluate numeric logarithms to whole numbers and prove using exponents.
  4. Identify and explain domain restrictions of logarithms.

Tips for Teachers


  • Watch the video “How I Feel About Logarithms” by Vi Hart.
  • Be sure to reference the Richter scale, pH, and decibels as real-life applications of the logarithmic scale.
  • Students may need to review solving equations of the form $${2^x=8}$$ before they can fully access this lesson.
  • This lesson focuses on whole numbers. Note that the second anchor problem has three examples of negative or fractional arguments; this can serve as a preview of the next lesson, but there is no need to spend too much time on these.
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Anchor Problems

25-30 minutes


Problem 1

A colony of bacteria starts with 5 cells and grows so that it doubles in size every hour. How long will it be until there are 160 bacteria? How long will it be until there are 1,000 bacteria?

Guiding Questions

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Problem 2

Take a guess at what these statements are saying:

$${{{power}}_2(8){=3}}$$

$${{{power}}_2(32)=5}$$

$${{{power}}_3(9)=2}$$

$${{{power}}_3{(81)=4}}$$

$${{{power}}_5(25)=2}$$

 

Now, see if you can fill in the blanks:

$${{{power}}_2(16)=}$$ ____ $${{{power}}_{19}\left ( 1\over1000 \right )=}$$ ___
$${{{power}}_6(36)=}$$ ____ $${{power}}$$__$${(81)=2}$$
$${{power}}_5$$( ___ )$${=3}$$ $${{power}}$$___$${(81)=4}$$
$${{power}}_2$$( ___ )$${=-1}$$ $${{power}}_{16}$$( ___ )$${={3\over2}}$$

Guiding Questions

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References

f(t) Introducing Logs

Introducing Logs by Kate Nowak is made available on Function of Time under the CC BY-NC-SA 3.0 license. Accessed Feb. 22, 2018, 4:30 p.m..

Problem 3

What are possible value(s) for $$x$$ and $$y$$ that will make the statement true?

$$\mathrm{log}_x1=y$$

$$\mathrm{log}_xx=y$$

$$\mathrm{log}_x0=y$$

Guiding Questions

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Target Task

5-10 minutes


Problem 1

Why is it necessary to specify that $${0<b<1}$$ and $${b>1}$$ are valid values for the base $$b$$ in the expression $$\mathrm{log}_b(x)$$?

References

EngageNY Mathematics Algebra II > Module 3 > Topic B > Lesson 8Exit Ticket, Question #1

Algebra II > Module 3 > Topic B > Lesson 8 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem 2

Evaluate the following logarithms:

$${\mathrm{log}_3(81)}$$

$${\mathrm{log}_{11}(1)}$$

$${\mathrm{log}_9(9)}$$

References

EngageNY Mathematics Algebra II > Module 3 > Topic B > Lesson 8Exit Ticket, Question #2

Algebra II > Module 3 > Topic B > Lesson 8 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Include problems translating between logarithm form and exponential form.
  • Ask for logarithms that evaluate to $$0$$ and $$1$$
  • Include problems using variables, for instance, of the form $${\mathrm{log}_x8=3}$$ or $${\mathrm{log}_xx^4}$$.

Next

Describe and evaluate simple numeric logarithms (Part II).

Lesson 8
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Modeling with and Interpreting Exponential Functions

Topic B: Definition and Meaning of Logarithms

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