What Does Exponential Growth Really Mean?
- A polynomial like
: exponent is fixed, base changes - An exponential like
: base is fixed, exponent changes
At
Exponential functions eventually surpass any polynomial.
Structure of an Exponential Function
: vertical stretch/reflection, sets the y-intercept , : the base — determines growth or decay- Domain: all real numbers
- Range:
when
Graph of the Growth Function
The graph rises from near zero, passes through
Key Features of Exponential Functions
For
- y-intercept:
— plug in - HA:
(shifts with vertical translation) - Domain: all reals; Range:
when
The graph never crosses
Decay Function:
- Base:
, which is between 0 and 1 → decay
- y-intercept:
— same as - HA:
; domain: all reals; range:
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.
Transformations: Finding the Shifted Asymptote
Example:
y-intercept:
Horizontal asymptote: the
Range:
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.
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.
Answers to Practice: Key Features
: growth; y-int ; HA ; range : decay; y-int ; HA ; range : growth; y-int ; HA ; range
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.
Logarithm as the Inverse of Exponential
- If
passes through , , , ... - Then
passes through , , ,
Swap the x and y coordinates to build the log table from the exponential table.
Graph of
The graph rises from the vertical asymptote, crosses
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.
Exponential and Log as Mirror Images
The two graphs are reflections of each other across
Common Log and Natural Log
— base 10; used in pH, decibels, Richter scale — base ; used in growth models, calculus
Both share: x-intercept
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.
The Logarithm Keeps Growing — Watch Out
Common misconception:
| 1,000 | |
| 1,000,000 | |
The log has NO horizontal asymptote. It grows without bound — just very slowly.
Practice: State Logarithm Key Features
For each, state x-intercept, vertical asymptote, domain, and range:
Hint for #3: what transformation shifts the VA?
Answers to Logarithm Evaluation Practice
: x-int ; VA ; domain ; range all reals : x-int ; VA ; domain ; range all reals : x-int ; VA ; domain ; range all reals
Key Takeaways from This Lesson
Exponential
Logarithmic
Watch out: Exponential never crosses
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.