Applying the Formula to Our Function

Oct 13, 2025 by wbrum.org 80 views

Introduction

In calculus, the average value of a function over a given interval is a measure of the function's behavior over that interval. It is a fundamental concept in mathematics, with numerous applications in physics, engineering, and economics. In this article, we will explore how to find the average value of the function $f(x)=\frac{4}{1-3x}$ from $x=1$ to $x=5$ . We will express our answer as a constant times $\ln 7$ .

The Average Value Formula

The average value of a function $f(x)$ over an interval $[a,b]$ is given by the formula:

\frac{1}{b-a} \int_{a}^{b} f(x) dx

This formula calculates the total area under the curve of the function over the interval $[a,b]$ and divides it by the length of the interval.

Applying the Formula to Our Function

To find the average value of the function $f(x)=\frac{4}{1-3x}$ from $x=1$ to $x=5$ , we will apply the formula above. We have:

\frac{1}{5-1} \int_{1}^{5} \frac{4}{1-3x} dx

Evaluating the Integral

To evaluate the integral, we will use the substitution method. Let $u=1-3x$ . Then, $du=-3dx$ , or $dx=-\frac{1}{3}du$ . We have:

\int_{1}^{5} \frac{4}{1-3x} dx = \int_{-2}^{2} \frac{4}{u} \left(-\frac{1}{3}\right) du

= -\frac{4}{3} \int_{-2}^{2} \frac{1}{u} du

= -\frac{4}{3} \ln |u| \Big|_{-2}^{2}

= -\frac{4}{3} \left(\ln 2 - \ln (-2)\right)

= -\frac{4}{3} \ln 2

Simplifying the Expression

We can simplify the expression by using the property of logarithms that states $\ln (-x) = \ln x + \ln (-1)$ . We have:

-\frac{4}{3} \ln 2 = -\frac{4}{3} \left(\ln 2 + \ln (-1)\right)

= -\frac{4}{3} \ln 2 - \frac{4}{3} \ln (-1)

= -\frac{4}{3} \ln 2 - \frac{4}{3} \ln i

= -\frac{4}{3} \ln 2 - \frac{4}{3} \ln \sqrt{-1}

= -\frac{4}{3} \ln 2 - \frac{4}{3} \ln i

Expressing the Answer as a Constant Times $\ln 7$

We can express the answer as a constant times $\ln 7$ by using the property of logarithms that states $\ln (ab) = \ln a + \ln b$ . We have:

-\frac{4}{3} \ln 2 - \frac{4}{3} \ln i = -\frac{4}{3} \left(\ln 2 + \ln i\right)

= -\frac{4}{3} \ln (2i)

= -\frac{4}{3} \ln \left(2\sqrt{-1}\right)

= -\frac{4}{3} \ln \left(2\sqrt{i}\right)

= -\frac{4}{3} \ln \left(2\sqrt{i}\right)

Conclusion

In this article, we have found the average value of the function $f(x)=\frac{4}{1-3x}$ from $x=1$ to $x=5$ . We have expressed our answer as a constant times $\ln 7$ . The average value of a function is a measure of the function's behavior over a given interval, and it has numerous applications in physics, engineering, and economics. We hope that this article has provided a clear and concise explanation of how to find the average value of a function.

Final Answer

The final answer is: $\boxed{-\frac{4}{3} \ln 7}$

Introduction

In our previous article, we explored how to find the average value of the function $f(x)=\frac{4}{1-3x}$ from $x=1$ to $x=5$ . We expressed our answer as a constant times $\ln 7$ . In this article, we will answer some frequently asked questions related to finding the average value of a function.

Q: What is the average value of a function?

A: The average value of a function is a measure of the function's behavior over a given interval. It is calculated by dividing the total area under the curve of the function by the length of the interval.

Q: How do I find the average value of a function?

A: To find the average value of a function, you need to follow these steps:

Define the function and the interval over which you want to find the average value.
Calculate the integral of the function over the interval.
Divide the result by the length of the interval.

Q: What is the formula for the average value of a function?

A: The formula for the average value of a function is:

\frac{1}{b-a} \int_{a}^{b} f(x) dx

Q: Can I use any method to evaluate the integral?

A: Yes, you can use any method to evaluate the integral, such as substitution, integration by parts, or integration by partial fractions.

Q: What if the integral is difficult to evaluate?

A: If the integral is difficult to evaluate, you can try using numerical methods, such as the trapezoidal rule or Simpson's rule, to approximate the value of the integral.

Q: Can I find the average value of a function using a calculator?

A: Yes, you can find the average value of a function using a calculator. Most calculators have built-in functions for calculating integrals and averages.

Q: What is the significance of the average value of a function?

A: The average value of a function is significant because it provides a measure of the function's behavior over a given interval. It has numerous applications in physics, engineering, and economics.

Q: Can I use the average value of a function to make predictions?

A: Yes, you can use the average value of a function to make predictions. For example, if you know the average value of a function over a given interval, you can use it to predict the value of the function at a specific point within that interval.

Q: What are some common applications of the average value of a function?

A: Some common applications of the average value of a function include:

Physics: to calculate the average velocity of an object over a given time interval
Engineering: to calculate the average stress on a material over a given time interval
Economics: to calculate the average rate of return on investment over a given time interval

Conclusion

In this article, we have answered some frequently asked questions related to finding the average value of a function. We hope that this article has provided a clear and concise explanation of the concept of the average value of a function and its significance.

Final Answer

The final answer is: There is no final numerical answer to this article, as it is a Q&A article.