Use the correct formula for the average rate of change

Oct 13, 2025 by wbrum.org 8 views

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Introduction

The average rate of change of a function is a measure of how much the function changes over a given interval. It is calculated by finding the difference in the function's output values at two different points and dividing by the difference in the input values. In this article, we will find the average rate of change of the function $f(x) = x^2 + 9x$ from $x_1 = 2$ to $x_2 = 7$ .

What is the Average Rate of Change?

The average rate of change of a function $f(x)$ over an interval $[x_1, x_2]$ is given by the formula:

\text{Average Rate of Change} = \frac{f(x_2) - f(x_1)}{x_2 - x_1}

This formula calculates the difference in the function's output values at $x_2$ and $x_1$ , and then divides by the difference in the input values.

Finding the Average Rate of Change of $f(x) = x^2 + 9x$

To find the average rate of change of $f(x) = x^2 + 9x$ from $x_1 = 2$ to $x_2 = 7$ , we need to calculate the values of $f(x_1)$ and $f(x_2)$ .

Calculating $f(x_1)$

We are given that $x_1 = 2$ . To find $f(x_1)$ , we substitute $x_1$ into the function:

f(x_1) = f(2) = (2)^2 + 9(2) = 4 + 18 = 22

Calculating $f(x_2)$

We are given that $x_2 = 7$ . To find $f(x_2)$ , we substitute $x_2$ into the function:

f(x_2) = f(7) = (7)^2 + 9(7) = 49 + 63 = 112

Calculating the Average Rate of Change

Now that we have found $f(x_1)$ and $f(x_2)$ , we can calculate the average rate of change:

\text{Average Rate of Change} = \frac{f(x_2) - f(x_1)}{x_2 - x_1} = \frac{112 - 22}{7 - 2} = \frac{90}{5} = 18

Conclusion

In this article, we found the average rate of change of the function $f(x) = x^2 + 9x$ from $x_1 = 2$ to $x_2 = 7$ . The average rate of change is $\boxed{18}$ .

Example Use Cases

The average rate of change is an important concept in mathematics and has many practical applications. Here are a few example use cases:

Economics: The average rate of change can be used to calculate the rate of inflation or the rate of economic growth.
Physics: The average rate of change can be used to calculate the velocity or acceleration of an object.
Finance: The average rate of change can be used to calculate the rate of return on investment or the rate of interest on a loan.

Tips and Tricks

Here are a few tips and tricks to help you calculate the average rate of change:

Make sure to calculate the values of $f(x_1)$ and $f(x_2)$ correctly.
Use the correct formula for the average rate of change.
Check your units to make sure they are consistent.

Frequently Asked Questions

Here are a few frequently asked questions about the average rate of change:

What is the average rate of change?
- The average rate of change is a measure of how much a function changes over a given interval.
How do I calculate the average rate of change?
- To calculate the average rate of change, you need to find the difference in the function's output values at two different points and divide by the difference in the input values.
What are some example use cases for the average rate of change?
- The average rate of change has many practical applications, including economics, physics, and finance.

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Introduction

The average rate of change is a fundamental concept in mathematics that has many practical applications. In this article, we will answer some frequently asked questions about the average rate of change.

Q&A

Q: What is the average rate of change?

A: The average rate of change is a measure of how much a function changes over a given interval. It is calculated by finding the difference in the function's output values at two different points and dividing by the difference in the input values.

Q: How do I calculate the average rate of change?

A: To calculate the average rate of change, you need to follow these steps:

Find the values of $f(x_1)$ and $f(x_2)$ : Substitute $x_1$ and $x_2$ into the function to find the corresponding output values.
Calculate the difference in the output values: Subtract $f(x_1)$ from $f(x_2)$ to find the difference in the output values.
Calculate the difference in the input values: Subtract $x_1$ from $x_2$ to find the difference in the input values.
Divide the difference in the output values by the difference in the input values: This will give you the average rate of change.

Q: What are some example use cases for the average rate of change?

A: The average rate of change has many practical applications, including:

Economics: The average rate of change can be used to calculate the rate of inflation or the rate of economic growth.
Physics: The average rate of change can be used to calculate the velocity or acceleration of an object.
Finance: The average rate of change can be used to calculate the rate of return on investment or the rate of interest on a loan.

Q: What are some common mistakes to avoid when calculating the average rate of change?

A: Here are some common mistakes to avoid when calculating the average rate of change:

Make sure to calculate the values of $f(x_1)$ and $f(x_2)$ correctly: Double-check your calculations to make sure you have the correct values.
Use the correct formula for the average rate of change: Make sure to use the formula $\frac{f(x_2) - f(x_1)}{x_2 - x_1}$ to calculate the average rate of change.
Check your units to make sure they are consistent: Make sure that your units are consistent, such as meters per second or dollars per year.

Q: How do I apply the average rate of change in real-world scenarios?

A: The average rate of change can be applied in many real-world scenarios, such as:

Calculating the rate of inflation: The average rate of change can be used to calculate the rate of inflation over a given period of time.
Calculating the rate of return on investment: The average rate of change can be used to calculate the rate of return on investment over a given period of time.
Calculating the velocity or acceleration of an object: The average rate of change can be used to calculate the velocity or acceleration of an object over a given period of time.

Conclusion

In this article, we have answered some frequently asked questions about the average rate of change. We have covered topics such as how to calculate the average rate of change, example use cases, and common mistakes to avoid. We hope that this article has been helpful in understanding the concept of the average rate of change.

Tips and Tricks

Here are a few tips and tricks to help you apply the average rate of change in real-world scenarios:

Make sure to calculate the values of $f(x_1)$ and $f(x_2)$ correctly: Double-check your calculations to make sure you have the correct values.
Use the correct formula for the average rate of change: Make sure to use the formula $\frac{f(x_2) - f(x_1)}{x_2 - x_1}$ to calculate the average rate of change.
Check your units to make sure they are consistent: Make sure that your units are consistent, such as meters per second or dollars per year.

Frequently Asked Questions

Here are a few frequently asked questions about the average rate of change:

What is the average rate of change?
- The average rate of change is a measure of how much a function changes over a given interval.
How do I calculate the average rate of change?
- To calculate the average rate of change, you need to find the difference in the function's output values at two different points and divide by the difference in the input values.
What are some example use cases for the average rate of change?
- The average rate of change has many practical applications, including economics, physics, and finance.