How to Write an Exponential Function – A Step-by-Step Guide

How to Write an Exponential Function A Step-by-Step Guide

To write an exponential function, I first identify whether I’m dealing with growth or decay, as this will determine the sign of the rate of change.

An exponential function typically takes the form $f(x) = ab^{x}$, where $a$ represents the initial value, $b$ is the base that denotes the growth or decay factor, and (x) represents time.

For growth, the base $b$ is greater than one. If I’m examining a decaying quantity, such as a radioactive substance, I would use a base $b$ between zero and one, indicating a decrease over time.

Illustration of How to Write an Exponential Function

In assessing real-world scenarios like population growth, I need to consider that the rate of change is proportional to the current amount.

This means as the population increases, the rate at which it grows will also become larger, which is a characteristic feature of exponential functions.

By examining data points and their relations, I can derive both the initial value and the growth or decay factor to model the situation accurately with an exponential equation.

Now imagine you’ve tracked a bacterial colony’s growth and noticed it doubles every hour. Curious to predict its size at any given time? Stay tuned as we continue to unveil the magic of exponential functions to forecast such dynamic changes.

Writing an Exponential Functions

Exponential functions are a type of mathematical function that find many uses in real-life scenarios, such as compound interest calculations and population growth models. In terms of structure, they can be broadly formulated as:

$$ f(x) = ab^{x} $$

In this formula:

  • ( f(x) ) represents the value of the function at ( x )
  • ( a ) is the initial value when ( x = 0 )
  • ( b ) is the base of the exponential function, which determines its rate of growth or decay
  • ( x ) is the variable, typically representing time or another changing quantity

When writing an exponential function, if ( a ) is positive, the function will have a positive initial value. It’s crucial that ( b ) is also a positive value to ensure the function remains exponential.

For the function’s base, ( b ), if you have a situation like compound interest, using ( e ) (approximately 2.71828), known as Euler’s number, is common. This is especially true when the process is continuous.

Here’s an example using doubling growth:

( x )(Hours)( f(x) )(Bacteria)

The function could be written as:

$$ f(x) = 100 \cdot 2^{x} $$

I’d derive this by observing that the initial value is 100, and the base, the factor by which the bacteria doubles, is 2. I hope this helps you understand how to write your exponential functions and recognize their elements in various contexts.

Graphing Exponential Functions

When I graph an exponential function, I’m dealing with expressions that represent growth or decay. The typical form of an exponential function is ( y = ab^x ), where a represents the y-intercept and b is the growth multiplier.

Firstly, I assess the growth multiplier. If ( b > 1 ), the graph will show exponential growth. Conversely, if ( 0 < b < 1 ), it indicates exponential decay.

With this foundation, I create a table listing essential data points, guiding me as I plot the graph:


The domain (all possible x-values) is all real numbers, while the range (all possible y-values) is ( y > 0 ) if a is positive.

I also consider the horizontal asymptote, generally the x-axis ( y=0 ) for basic exponential functions. This line represents a boundary that the graph approaches but never touches.

When using a graphing calculator, I input the function and use these data points as a reference to check for accuracy. The slope of the curve is not constant; it depends on the function’s base. It steepens or flattens as it moves depending on whether the function represents growth or decay.

Remember, each point on the graph represents a solution to the exponential equation. By thoroughly understanding and plotting several points, I can accurately sketch the exponential function, providing a visual representation of the function’s behavior.

Comparing Growth Types

The main differences between linear growth and exponential growth are their rates of change. Linear growth increases by a constant amount, while exponential growth multiplies by a constant factor, leading to a much faster increase over time.

In linear growth, the increase is steady. You can describe linear growth with a linear function of the form (y = mx + b), where (m) is the rate of growth and (b) is the starting value. This rate doesn’t change; if (m) equals 2, then the function grows by 2 with each step. A graph of a linear function is a straight line, showcasing this uniformity.

Exponential growth, however, is characterized by its growth factor. A typical exponential equation looks like (y = a \cdot b^x), where (a) represents the initial amount, (b) is the growth factor, and (x) is the time elapsed. Unlike the straight path of linear functions, exponential functions curve upward, increasing rapidly as time goes on. When (b) is greater than 1, the function represents growth, such as doubling if (b = 2), where the amount doubles with each step. If (b) is between 0 and 1, it represents decay.

I’ll illustrate with a simple comparison:

  • Linear: Starting with \$50, if I add \$10 every day, the sequence is \$50, \$60, \$70…
  • Exponential: Starting with \$50, if I double the amount every day, the sequence is \$50, \$100, \$200…

This stark contrast demonstrates why understanding the differences is crucial in fields like finance, biology, and physics, where growth types have vast implications.

Application of Exponential Functions

When I’m dealing with situations involving continuous growth or decay, I often turn to exponential functions. They are incredibly effective for modeling phenomena like population growth, radioactive decay, or how money accrues interest in a bank account. Let me show you how this works with some example contexts.

Population Growth: Imagine a small town with a population that doubles every year. If the initial population is 500 people, the growth after ( t ) years can be described by $P(t) = 500 \times 2^t $. This demonstrates exponential growth because the rate of increase becomes faster over time.

Compound Interest: Money grows in a bank account with compound interest – one of the most delightful applications for those who save!

If I have \$1000 in an account with a 5% annual interest rate, compounded yearly, the amount of money after ( n ) years is calculated with the formula $A = 1000 \times (1 + \frac{0.05}{1})^{1 \times n}$, where ( A ) represents the amount of money accrued.

Continuous Growth: Now, to illustrate continuous growth in a more abstract sense, mathematicians use the natural base ( e ).

This base is especially prominent when dealing with continuous processes. For example, if a bacteria culture grows continuously at a rate of 20% per hour, we express this as $N(t) = N_0 e^{0.2t}$, where $ N_0$ is the initial amount of bacteria.

Here’s a handy table summarizing the formulas:

Population Growth$P(t) = P_0 \times b^t$
Money (Compound Interest)v A = P \times \left(1 + \frac{r}{n}\right)^{nt} $
Continuous Growth$N(t) = N_0 e^{rt}$

Each time I use these functions, I’m fascinated by their predictive power in describing the real world around us.


In wrapping up our exploration, I’ve aimed to equip you with the understanding necessary to craft an exponential function from scratch.

Remember, these functions are the bedrock for modeling phenomena exhibiting rapid growth or decay, such as populations, investments, or radioactive decay.

To quickly recapitulate, you pin down the initial value ( a ) and the base ( b ) of the exponential function $ f(x) = a \cdot b^x $, which are integral to shaping the curve’s trajectory.

Empower yourself to experiment with different values to observe the diverse effects on growth and decay patterns; it’s an excellent method to internalize the fundamentals of exponential functions. If you persist with practice and apply these concepts to real-world scenarios, the process becomes second nature.

I encourage you to remain curious—dive into complex problems and leverage your newfound skills to describe the world in exponential terms. As mathematical concepts can be abstract, hands-on practice is your key to mastering the subject.

Whether you’re a student, a professional, or simply a math enthusiast, the ability to construct an exponential function is a powerful tool in your arsenal. Let’s keep the numbers rolling and our mathematical journey thriving.