1 / 24
Exponential and Logarithmic Functions | Lesson 1 of 2

Graphing Exponential and Logarithmic Functions

Lesson 1 of 2: Exponential and Log Families

In this lesson:

  • Graph exponential functions and identify key features
  • Distinguish growth from decay using the base
  • Graph logarithmic functions as inverses of exponentials
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Learning Objectives for This Lesson

By the end of this lesson, you will:

  1. Graph ; identify y-int, HA, domain, range
  2. Distinguish growth () from decay ()
  3. Graph ; identify x-int, VA, domain, range
  4. Connect exponential and log functions as inverses
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

What Does Exponential Growth Really Mean?

  • A polynomial like : exponent is fixed, base changes
  • An exponential like : base is fixed, exponent changes

At : but .

Exponential functions eventually surpass any polynomial.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Structure of an Exponential Function

  • : vertical stretch/reflection, sets the y-intercept
  • , : the base — determines growth or decay
  • Domain: all real numbers
  • Range: when
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Graph of the Growth Function

J-curve graph of f(x) = 2^x showing exponential growth with horizontal asymptote at y=0

The graph rises from near zero, passes through , and grows steeply.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Key Features of Exponential Functions

For :

  • y-intercept: — plug in
  • HA: (shifts with vertical translation)
  • Domain: all reals; Range: when

The graph never crosses .

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Decay Function:

  • Base: , which is between 0 and 1 → decay

Decay curve g(x) = (1/2)^x showing reverse J-shape descending from upper left to horizontal asymptote at y=0

  • y-intercept: — same as
  • HA: ; domain: all reals; range:
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Growth Versus Decay: Role of the Base

Base Behavior Direction
Exponential growth Rises from left to right
Exponential decay Falls from left to right

Same features, opposite directions — the base tells you which.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Transformations: Finding the Shifted Asymptote

Example:

y-intercept:

Horizontal asymptote: the shifts HA to

Range:

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Quick Check: Growth, Decay, or Neither?

  • Is this growth or decay?
  • What is the horizontal asymptote?
  • What is the y-intercept?

Think through each question, then advance for the answers.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Practice: Classify and Identify Key Features

For each, classify as growth or decay and state y-intercept, HA, and range:

Pause and work through each before the next slide.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Answers to Practice: Key Features

  1. : growth; y-int ; HA ; range
  2. : decay; y-int ; HA ; range
  3. : growth; y-int ; HA ; range
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Bridge: From Exponential to Logarithmic

Exponential functions grow toward infinity.

  • has a horizontal asymptote at
  • The inverse of must swap x and y
  • What was a horizontal boundary becomes a vertical boundary

Every feature of the exponential maps to a mirrored feature in the logarithm.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Logarithm as the Inverse of Exponential

is defined as the inverse of

  • If passes through , , , ...
  • Then passes through , , ,

Swap the x and y coordinates to build the log table from the exponential table.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Graph of

Logarithm graph showing f(x) = log₂(x) rising steeply near x=0 then flattening, with vertical asymptote at x=0

The graph rises from the vertical asymptote, crosses , then flattens.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Key Features of Logarithmic Functions

For :

  • x-intercept: — since for any base
  • Vertical asymptote:
  • Domain: ; Range: all reals

Exponential has y-int and HA; log has x-int and VA — features swap.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Exponential and Log as Mirror Images

Both 2^x and log₂(x) plotted on same axes with the line y=x shown as the mirror line

The two graphs are reflections of each other across .

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Common Log and Natural Log

  • — base 10; used in pH, decibels, Richter scale
  • — base ; used in growth models, calculus

Both share: x-intercept , VA , domain .

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Quick Check: Identify Logarithm Key Features

  • Where does this graph cross the x-axis?
  • What is the vertical asymptote?
  • What is the domain? The range?

Try each before the next slide — use the general formulas.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

The Logarithm Keeps Growing — Watch Out

Common misconception: approaches a horizontal asymptote.

1,000
1,000,000

The log has NO horizontal asymptote. It grows without bound — just very slowly.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Practice: State Logarithm Key Features

For each, state x-intercept, vertical asymptote, domain, and range:

Hint for #3: what transformation shifts the VA?

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Answers to Logarithm Evaluation Practice

  1. : x-int ; VA ; domain ; range all reals
  2. : x-int ; VA ; domain ; range all reals
  3. : x-int ; VA ; domain ; range all reals
Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Key Takeaways from This Lesson

Exponential : y-int ; HA ; → growth; → decay

Logarithmic : x-int ; VA ; inverse of

Watch out: Exponential never crosses . Log has no HA — it keeps growing.

Grade 9 Algebra | HSF.IF.C.7.e
Exponential and Logarithmic Functions | Lesson 1 of 2

Up Next: Trig Functions and Family Comparison

In Lesson 2, you will:

  • Graph and
  • Identify amplitude, period, and midline
  • Compare exponential, logarithmic, and trigonometric functions side by side

You've mastered two of the three families — one more to go.

Grade 9 Algebra | HSF.IF.C.7.e