Exponential Modeling and Logarithms

Lesson 1

Math

Unit 5

11th Grade

Lesson 1 of 16

Objective


Identify, model, and analyze geometric sequences.

Common Core Standards


Core Standards

  • F.IF.A.3 — Recognize that sequences are functions, sometimes defined recursively, whose domain is a subset of the integers. For example, the Fibonacci sequence is defined recursively by f(0) = f(1) = 1, f(n+1) = f(n) + f(n-1) for n ≥ 1.
  • F.IF.B.5 — Relate the domain of a function to its graph and, where applicable, to the quantitative relationship it describes. For example, if the function h(n) gives the number of person-hours it takes to assemble n engines in a factory, then the positive integers would be an appropriate domain for the function. Modeling is best interpreted not as a collection of isolated topics but in relation to other standards. Making mathematical models is a Standard for Mathematical Practice, and specific modeling standards appear throughout the high school standards indicated by a star symbol (★). The star symbol sometimes appears on the heading for a group of standards; in that case, it should be understood to apply to all standards in that group.
  • F.LE.A.2 — Construct linear and exponential functions, including arithmetic and geometric sequences, given a graph, a description of a relationship, or two input-output pairs (include reading these from a table).

Foundational Standards

  • F.LE.A.1.A
  • F.LE.A.1.B
  • F.LE.A.1.C

Criteria for Success


  • Define geometric sequences and identify similarities with exponential functions.
  • Identify domain restrictions for geometric sequences.
  • Identify features of geometric sequences including domain, rate of growth or decay, y-intercepts, and asymptotes, from tables, equations, and graphs.
  • Write equations for sequences using the forms $${a(n)=a(0)\times r^{n}}$$ or $${a(n)=a(1) \times r^{n-1}}$$.

Tips for Teachers


The Common Core Standards call for using function notation with sequences to reinforce the idea that sequences are just another type of function. Students preparing for calculus courses will benefit from also seeing subscript form, written $${a_{n}=a_{0} \times r^{n}}$$ or $${a_{n}=a_{1} \times r^{n-1}}$$.

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Anchor Problems


Problem 1

Below is a visual representation of a pattern of growth of a particular kind of bacterium.

How many bacteria are there after 20 minutes?

Guiding Questions

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References

Mathematics Vision Project: Secondary Mathematics One Module 3: Arithmetic and Geometric SequencesImage from 3.2 Growing, Growing Dots

Module 3: Arithmetic and Geometric Sequences from Secondary Mathematics One: An Integrated Approach made available by Mathematics Vision Project under the CC BY 4.0 license. © 2016 Mathematics Vision Project. Accessed Feb. 22, 2018, 2:01 p.m..

Problem 2

Have students complete Dan Meyer's Three-Act Task Incredible Shrinking Dollar.

Guiding Questions

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References

Dan Meyer's Three-Act Math Incredible Shrinking Dollar

Incredible Shrinking Dollar by Dan Meyer is licensed under the CC BY 3.0 license. Accessed Feb. 27, 2018, 8:56 a.m..

Problem 3

Show that the following two functions are equivalent:

$${f(n)=3(2)^{x-1}}$$ and $${f(n)=1.5(2)^x}$$

Guiding Questions

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Target Task


 Write a function for the following geometric sequence, where $${f(1)=216}$$.

$${216, 108, 54, 27, ...}$$

$${{f(n)=}}$$ _____ (_____)$${^n}$$

$${{f(n)=}}$$ _____ (_____)$${^{n-1}}$$

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 moving between lists, tables, graphs, and equations.
  • Include problems writing sequences as equations in different forms.
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Lesson 2

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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