Math Problem Statement

Determine where the absolute extrema of f(x) = 3x^(2/3) - 2x on the interval [-1, 1] occur.

Solution

To determine the absolute extrema of f(x)=3x2/32xf(x) = 3x^{2/3} - 2x on the interval [1,1][-1, 1], we'll follow these steps:

  1. Find the derivative of f(x)f(x) to locate any critical points within the interval.
  2. Evaluate the function at the critical points and endpoints to determine the absolute maximum and minimum values.

Step 1: Differentiate f(x)f(x)

Given: f(x)=3x2/32xf(x) = 3x^{2/3} - 2x

The derivative f(x)f'(x) is: f(x)=323x1/32=2x1/32f'(x) = 3 \cdot \frac{2}{3} x^{-1/3} - 2 = 2x^{-1/3} - 2 Simplifying, we get: f(x)=2x1/32f'(x) = \frac{2}{x^{1/3}} - 2

Step 2: Set f(x)=0f'(x) = 0 to find critical points

2x1/32=0\frac{2}{x^{1/3}} - 2 = 0 Solving for xx: 2x1/3=2\frac{2}{x^{1/3}} = 2 x1/3=1x=1x^{1/3} = 1 \Rightarrow x = 1

So, x=1x = 1 is a critical point. Note also that f(x)f'(x) is undefined at x=0x = 0, so x=0x = 0 is another point to check.

Step 3: Evaluate f(x)f(x) at the endpoints and critical points

We need to evaluate f(x)f(x) at x=1x = -1, x=0x = 0, and x=1x = 1.

  1. At x=1x = -1: f(1)=3(1)2/32(1)=31+2=5f(-1) = 3(-1)^{2/3} - 2(-1) = 3 \cdot 1 + 2 = 5

  2. At x=0x = 0: f(0)=302/320=0f(0) = 3 \cdot 0^{2/3} - 2 \cdot 0 = 0

  3. At x=1x = 1: f(1)=312/321=32=1f(1) = 3 \cdot 1^{2/3} - 2 \cdot 1 = 3 - 2 = 1

Conclusion

The absolute maximum value of f(x)f(x) on [1,1][-1, 1] is 55 at x=1x = -1.
The absolute minimum value of f(x)f(x) on [1,1][-1, 1] is 00 at x=0x = 0.

Answers:

  1. The absolute maximum occurs at x=1x = -1.
  2. The absolute minimum occurs at x=0x = 0.

Would you like further clarification or details?


Here are five related questions for further practice:

  1. How do you find critical points for functions with fractional exponents?
  2. Why does the function have an undefined derivative at x=0x = 0?
  3. What is the significance of evaluating at endpoints for absolute extrema?
  4. How can we use the second derivative to classify critical points?
  5. How would the process change if the interval were open instead of closed?

Tip: Always check endpoints in a closed interval when finding absolute extrema, as they can often hold the maximum or minimum values.

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Math Problem Analysis

Mathematical Concepts

Calculus
Absolute Extrema
Critical Points
Endpoints Evaluation

Formulas

f'(x) = 2x^(-1/3) - 2

Theorems

Extreme Value Theorem

Suitable Grade Level

Grades 11-12