Chapter 3: Problem 18
Find (without using a calculator) the absolute extreme values of each function on the given interval. $$ f(x)=\sqrt[3]{x^{2}} \text { on }[-1,8] $$
Short Answer
Expert verified
The absolute minimum is 0 at \( x = 0 \), and the absolute maximum is 4 at \( x = 8 \).
Step by step solution
01
Find the derivative of the function
To find the critical points of the function, we start by finding the derivative of the function \( f(x) = \sqrt[3]{x^2} = x^{2/3} \). Using the power rule for differentiation, the derivative is \( f'(x) = \frac{2}{3}x^{-1/3} = \frac{2}{3x^{1/3}} \).
02
Find critical points
The critical points occur where the derivative is zero or undefined. The derivative \( \frac{2}{3x^{1/3}} \) is never zero, but it is undefined when the denominator is zero. This happens at \( x = 0 \). Thus, \( x = 0 \) is a critical point.
03
Evaluate the function at the endpoints
To find the absolute extremum, evaluate the function at both endpoints of the interval \([-1, 8]\) and at any critical points. Start with the endpoints:- For \( x = -1 \), \( f(-1) = \sqrt[3]{(-1)^2} = 1 \).- For \( x = 8 \), \( f(8) = \sqrt[3]{8^2} = \sqrt[3]{64} = 4 \).
04
Evaluate the function at the critical point
Evaluate the function at the critical point found in Step 2:- For \( x = 0 \), \( f(0) = \sqrt[3]{0^2} = 0 \).
05
Determine the absolute extrema
Now compare the values of \( f(x) \) evaluated at the endpoints and the critical point. We have:- \( f(-1) = 1 \)- \( f(0) = 0 \)- \( f(8) = 4 \)The smallest value is \( 0 \) at \( x = 0 \), and the largest value is \( 4 \) at \( x = 8 \). Thus, the absolute minimum is 0 at \( x = 0 \), and the absolute maximum is 4 at \( x = 8 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding Critical Points
Critical points in a function are where the derivative is zero or undefined. They are crucial in finding the extrema (minimum or maximum values) of the function. For our function, \( f(x) = \sqrt[3]{x^2} \), the derivative simplifies to \( f'(x) = \frac{2}{3x^{1/3}} \). This derivative offers insights into the behavior of the function.
- The derivative is never zero because \( \frac{2}{3x^{1/3}} \) has no numerator that solves to zero.
- It's undefined where the denominator is zero; precisely, at \( x = 0 \). Here, the cube root of zero in the denominator makes the expression undefined.
Grasping the Derivative
The derivative of a function represents the rate at which the function's value changes. Using the power rule, we identified the derivative of \( f(x) = \sqrt[3]{x^2} \) to be \( f'(x) = \frac{2}{3x^{1/3}} \).
- This tells us how the function grows or decreases at any point along the curve.
- It acts as a tool to pinpoint critical points where potential extrema might occur on an interval.
Interval Evaluation Method
Interval evaluation is about examining function values over a specified range. In the given problem, the interval is \([-1, 8]\). These endpoints bound the area in which we search for extrema.
- First, evaluate the function at both endpoints of the interval.
- Determine function values at any critical points within this range.
- Compare these values to find which is the largest and smallest.
Comprehensive Function Analysis
Function analysis involves multiple steps, including finding critical points and evaluating the function.
- Derivatives highlight critical points, showing where the function might have peaks and troughs.
- Endpoint evaluations confirm these observations within a given interval.
- Finally, comparing results identifies absolute extrema; the maximum and minimum values the function can take.