Chapter 4: Problem 46
41-54 Find the absolute maximum and absolute minimum values of f on the given interval. $$f(x)=\left(x^{2}-1\right)^{3}, \quad[-1,2]$$
Short Answer
Expert verified
Max is 27 at x=2; min is -1 at x=0.
Step by step solution
01
Identify the function and interval
The function given is \( f(x) = (x^2 - 1)^3 \), and we need to find the absolute maximum and minimum on the interval \([-1, 2]\).
02
Find the derivative
Differentiate the function to find the critical points. Let \( u = x^2 - 1 \), then \( f(x) = u^3 \). Using the chain rule, the derivative is \( f'(x) = 3u^2 \cdot u' \), where \( u' = 2x \). Thus, \( f'(x) = 3(x^2 - 1)^2 \times 2x = 6x(x^2 - 1)^2 \).
03
Set the derivative to zero
Set \( f'(x) = 6x(x^2 - 1)^2 = 0 \) to find critical points. Solve for \( x \):- \( 6x = 0 \) yields \( x = 0 \)- \( (x^2 - 1)^2 = 0 \) yields \( x^2 - 1 = 0 \), so \( x = \pm 1 \).
04
Evaluate the function at critical points and endpoints
Evaluate \( f(x) \) at \( x = -1, 0, 1, 2 \):- \( f(-1) = ((-1)^2 - 1)^3 = 0^3 = 0 \)- \( f(0) = (0^2 - 1)^3 = (-1)^3 = -1 \)- \( f(1) = (1^2 - 1)^3 = 0^3 = 0 \)- \( f(2) = (2^2 - 1)^3 = 3^3 = 27 \)
05
Determine absolute maximum and minimum
From the evaluations in Step 4, compare values:- The absolute maximum value is \( 27 \) at \( x = 2 \).- The absolute minimum value is \( -1 \) at \( x = 0 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Critical Points
In calculus, critical points occur where the derivative of a function is zero or undefined. These points are essential as they can indicate where a function's behavior changes, such as turning from increasing to decreasing or vice versa. They are important in finding absolute extrema (maximum or minimum values) on a given interval.
A function's critical points are found by first taking the derivative and then setting it equal to zero. In our case, the function is given by \( f(x) = (x^2 - 1)^3 \).
A function's critical points are found by first taking the derivative and then setting it equal to zero. In our case, the function is given by \( f(x) = (x^2 - 1)^3 \).
- First, we find the derivative \( f'(x) \) and set it equal to zero: \( 6x (x^2 - 1)^2 = 0 \).
- This equation gives us potential points of interest: \( x = 0 \) and \( x = \pm 1 \).
Derivative
The derivative of a function provides vital information on the rate of change at any given point within the function. It can highlight where a function is increasing or decreasing.
In our exercise, finding the derivative of \( f(x) = (x^2 - 1)^3 \) involves using the chain rule.
In our exercise, finding the derivative of \( f(x) = (x^2 - 1)^3 \) involves using the chain rule.
- We first set \( u = x^2 - 1 \), thus transforming the function into \( u^3 \).
- The derivative \( f'(x) = 3u^2 \cdot (2x) \) simplifies the process.
- Finally, substituting back, we get \( f'(x) = 6x (x^2 - 1)^2 \).
Interval Evaluation
Interval evaluation is a technique used to examine points across a predefined range to determine the extremal values of a function. It involves calculating the function's value at both the critical points and the interval endpoints. In this case, we evaluate the function \( f(x) = (x^2 - 1)^3 \) at the critical points \( x = -1, 0, 1 \), and the interval endpoints \( x = -1, 2 \):
- \( f(-1) = ((-1)^2 - 1)^3 = 0 \)
- \( f(0) = (0^2 - 1)^3 = -1 \)
- \( f(1) = (1^2 - 1)^3 = 0 \)
- \( f(2) = (2^2 - 1)^3 = 27 \)
Chain Rule
The chain rule is a fundamental derivative rule used when differentiating composite functions. A composite function arises when one function is applied to the result of another.In this exercise, our original function \( f(x) = (x^2 - 1)^3 \) involves such a composition. We need to differentiate it using the chain rule.
- First, identify the inner function and outer function: \( u = x^2 - 1 \), so \( f(u) = u^3 \).
- Differentiate the outer function \( 3u^2 \), then multiply by the derivative of the inner function \( u' = 2x \), giving \( 6x(x^2 - 1)^2 \).