Critical Values on the Interval

Oct 13, 2025 by wbrum.org 133 views

Introduction

In calculus, critical values are points on a function where the derivative is zero or undefined. These points are crucial in understanding the behavior of a function, particularly in optimization problems. In this article, we will explore how to find critical values of a given function on a closed interval.

The Function

The given function is $f(x) = x^4 - 32x^2 + 8$ . We are interested in finding critical values on the closed interval $[-3, 7]$ .

Step 1: Find the Derivative

To find critical values, we need to find the derivative of the function. Using the power rule, we get:

f'(x) = 4x^3 - 64x

Step 2: Set the Derivative Equal to Zero

To find critical values, we set the derivative equal to zero and solve for $x$ :

4x^3 - 64x = 0

We can factor out $4x$ :

4x(x^2 - 16) = 0

This gives us two possible solutions:

4x = 0 \quad \text{or} \quad x^2 - 16 = 0

Step 3: Solve for x

Solving for $x$ in both equations, we get:

x = 0 \quad \text{or} \quad x^2 = 16

Taking the square root of both sides, we get:

x = \pm 4

Step 4: Check for Undefined Derivative

We also need to check if the derivative is undefined at any point on the interval. In this case, the derivative is a polynomial, so it is defined everywhere.

Step 5: List Critical Values

The critical values are the points where the derivative is zero or undefined. In this case, the critical values are:

x = -4, 0, 4

Conclusion

In conclusion, we have found the critical values of the function $f(x) = x^4 - 32x^2 + 8$ on the closed interval $[-3, 7]$ . The critical values are $x = -4, 0, 4$ .

Critical Values on the Interval

To find the critical values on the interval $[-3, 7]$ , we need to check if the critical values are within the interval. In this case, all three critical values are within the interval.

Final Answer

$The final answer is: $\boxed{-4, 0, 4}$<br/> **Q&A: Finding Critical Values of a Function on a Closed Interval**$

Introduction

In our previous article, we explored how to find critical values of a function on a closed interval. In this article, we will answer some frequently asked questions related to finding critical values.

Q: What is a critical value?

A critical value is a point on a function where the derivative is zero or undefined. These points are crucial in understanding the behavior of a function, particularly in optimization problems.

Q: How do I find the derivative of a function?

To find the derivative of a function, you can use the power rule, which states that if $f(x) = x^n$ , then $f'(x) = nx^{n-1}$ . You can also use other rules, such as the product rule and the quotient rule.

Q: What is the difference between a critical value and a local maximum or minimum?

A critical value is a point where the derivative is zero or undefined, while a local maximum or minimum is a point where the function has a maximum or minimum value. Not all critical values are local maxima or minima, and not all local maxima or minima are critical values.

Q: How do I determine if a critical value is a local maximum or minimum?

To determine if a critical value is a local maximum or minimum, you can use the second derivative test. If the second derivative is positive at a critical value, then the critical value is a local minimum. If the second derivative is negative at a critical value, then the critical value is a local maximum.

Q: What if the second derivative is zero at a critical value?

If the second derivative is zero at a critical value, then the second derivative test is inconclusive. In this case, you may need to use other methods, such as the first derivative test or the graphing method, to determine if the critical value is a local maximum or minimum.

Q: Can I use the first derivative test to determine if a critical value is a local maximum or minimum?

Yes, you can use the first derivative test to determine if a critical value is a local maximum or minimum. If the first derivative changes from positive to negative at a critical value, then the critical value is a local maximum. If the first derivative changes from negative to positive at a critical value, then the critical value is a local minimum.

Q: What if the function has multiple critical values?

If the function has multiple critical values, then you need to examine each critical value separately to determine if it is a local maximum or minimum.

Q: Can I use technology to find critical values?

Yes, you can use technology, such as a graphing calculator or a computer algebra system, to find critical values. These tools can help you visualize the function and find the critical values.

Conclusion

In conclusion, finding critical values of a function on a closed interval is an important concept in calculus. By understanding how to find critical values, you can better analyze and understand the behavior of a function.

Common Mistakes to Avoid

Not checking if the derivative is zero or undefined at a point
Not using the second derivative test to determine if a critical value is a local maximum or minimum
Not examining each critical value separately
Not using technology to find critical values

Final Tips

Always check if the derivative is zero or undefined at a point
Use the second derivative test to determine if a critical value is a local maximum or minimum
Examine each critical value separately
Use technology to find critical values

Additional Resources

Calculus textbooks
Online resources, such as Khan Academy and MIT OpenCourseWare
Graphing calculators and computer algebra systems