Determine the interval of the domain

Oct 13, 2025 by wbrum.org 26 views

Introduction

In mathematics, a piecewise-defined function is a function that is defined by multiple sub-functions, each applied to a specific interval of the domain. These functions are commonly used to model real-world phenomena that exhibit different behaviors in different regions. In this article, we will explore the concept of piecewise-defined functions and provide a step-by-step guide on how to evaluate them.

What is a Piecewise-Defined Function?

A piecewise-defined function is a function that is defined by multiple sub-functions, each applied to a specific interval of the domain. The function is typically defined using a combination of if-then statements, where each statement specifies the interval of the domain and the corresponding sub-function.

Example: Evaluating a Piecewise-Defined Function

Let's consider the piecewise-defined function:

f(x)=\begin{cases} 1-4x & \text{if } x \leq -3 \\ 4x & \text{if } -3 \ \textless \ x \ \textless \ 8 \\ 5x+2 & \text{if } x \geq 8 \end{cases}

To evaluate this function, we need to determine which sub-function to use based on the value of $x$ . If $x$ is less than or equal to $-3$ , we use the first sub-function, $1-4x$ . If $x$ is greater than $-3$ but less than $8$ , we use the second sub-function, $4x$ . If $x$ is greater than or equal to $8$ , we use the third sub-function, $5x+2$ .

Step-by-Step Guide to Evaluating a Piecewise-Defined Function

To evaluate a piecewise-defined function, follow these steps:

Determine the interval of the domain: Identify the interval of the domain that corresponds to the given value of $x$ .
Choose the corresponding sub-function: Select the sub-function that corresponds to the interval of the domain.
Evaluate the sub-function: Evaluate the sub-function using the given value of $x$ .
Return the result: Return the result of the evaluation.

Example Evaluations

Let's evaluate the piecewise-defined function for different values of $x$ .

Evaluating $f(-4)$

To evaluate $f(-4)$ , we need to determine which sub-function to use. Since $-4$ is less than or equal to $-3$ , we use the first sub-function, $1-4x$ .

f(-4) = 1-4(-4) = 1+16 = 17

Evaluating $f(2)$

To evaluate $f(2)$ , we need to determine which sub-function to use. Since $2$ is greater than $-3$ but less than $8$ , we use the second sub-function, $4x$ .

f(2) = 4(2) = 8

Evaluating $f(10)$

To evaluate $f(10)$ , we need to determine which sub-function to use. Since $10$ is greater than or equal to $8$ , we use the third sub-function, $5x+2$ .

f(10) = 5(10)+2 = 50+2 = 52

Conclusion

Common Mistakes to Avoid

When evaluating piecewise-defined functions, it's essential to avoid common mistakes such as:

Incorrectly identifying the interval of the domain: Make sure to identify the correct interval of the domain that corresponds to the given value of $x$ .
Choosing the wrong sub-function: Select the correct sub-function that corresponds to the interval of the domain.
Evaluating the wrong sub-function: Evaluate the correct sub-function using the given value of $x$ .

Real-World Applications

Piecewise-defined functions have numerous real-world applications, including:

Modeling population growth: Piecewise-defined functions can be used to model population growth, where the growth rate changes over time.
Modeling economic systems: Piecewise-defined functions can be used to model economic systems, where the behavior of the system changes over time.
Modeling physical systems: Piecewise-defined functions can be used to model physical systems, where the behavior of the system changes over time.

Final Thoughts

Q&A: Evaluating Piecewise-Defined Functions

Q: What is a piecewise-defined function?

A: A piecewise-defined function is a function that is defined by multiple sub-functions, each applied to a specific interval of the domain.

Q: How do I determine which sub-function to use?

A: To determine which sub-function to use, you need to identify the interval of the domain that corresponds to the given value of $x$ . Then, select the sub-function that corresponds to that interval.

Q: What if the value of $x$ is not in any of the intervals?

A: If the value of $x$ is not in any of the intervals, the function is undefined for that value of $x$ .

Q: Can I have multiple sub-functions for the same interval?

A: No, you cannot have multiple sub-functions for the same interval. Each interval must have a unique sub-function.

Q: How do I evaluate a piecewise-defined function?

A: To evaluate a piecewise-defined function, follow these steps:

Determine the interval of the domain that corresponds to the given value of $x$ .
Choose the corresponding sub-function.
Evaluate the sub-function using the given value of $x$ .
Return the result.

Q: What if I make a mistake when evaluating a piecewise-defined function?

A: If you make a mistake when evaluating a piecewise-defined function, you may get an incorrect result. To avoid this, make sure to:

Identify the correct interval of the domain.
Choose the correct sub-function.
Evaluate the correct sub-function.

Q: Can I use piecewise-defined functions to model real-world phenomena?

A: Yes, piecewise-defined functions can be used to model real-world phenomena that exhibit different behaviors in different regions.

Q: What are some common applications of piecewise-defined functions?

A: Some common applications of piecewise-defined functions include:

Modeling population growth
Modeling economic systems
Modeling physical systems

Q: How do I graph a piecewise-defined function?

A: To graph a piecewise-defined function, you need to graph each sub-function separately and then combine them into a single graph.

Q: Can I use piecewise-defined functions to solve optimization problems?

A: Yes, piecewise-defined functions can be used to solve optimization problems. For example, you can use piecewise-defined functions to model the cost of producing a product and then optimize the production level to minimize the cost.

Q: What are some common mistakes to avoid when working with piecewise-defined functions?

A: Some common mistakes to avoid when working with piecewise-defined functions include:

Incorrectly identifying the interval of the domain
Choosing the wrong sub-function
Evaluating the wrong sub-function

Conclusion

In conclusion, piecewise-defined functions are a powerful tool for modeling real-world phenomena that exhibit different behaviors in different regions. By following the step-by-step guide outlined in this article, you can evaluate piecewise-defined functions with confidence. Remember to avoid common mistakes and explore real-world applications to deepen your understanding of piecewise-defined functions.

Additional Resources

For more information on piecewise-defined functions, check out the following resources:

Khan Academy: Piecewise-defined functions
Mathway: Piecewise-defined functions
Wolfram MathWorld: Piecewise-defined functions