Math Problem Statement

The absolute minimum value of the function f(x)=10x(2−ln x) on the interval [1,e^2]is

Solution

To find the absolute minimum value of the function f(x)=10x(2lnx)f(x) = 10x(2 - \ln x) on the interval [1,e2][1, e^2], we follow these steps:

Step 1: Find the derivative of f(x)f(x)

We need to differentiate the function f(x)=10x(2lnx)f(x) = 10x(2 - \ln x).

First, apply the product rule: f(x)=ddx[10x](2lnx)+10xddx(2lnx)f'(x) = \frac{d}{dx} [10x] \cdot (2 - \ln x) + 10x \cdot \frac{d}{dx} (2 - \ln x)

f(x)=10(2lnx)+10x(1x)f'(x) = 10(2 - \ln x) + 10x \cdot (-\frac{1}{x})

f(x)=10(2lnx)10f'(x) = 10(2 - \ln x) - 10

f(x)=2010lnx10f'(x) = 20 - 10\ln x - 10

f(x)=10(1lnx)f'(x) = 10(1 - \ln x)

Step 2: Find the critical points

Set the derivative equal to zero to find the critical points: 10(1lnx)=010(1 - \ln x) = 0

1lnx=01 - \ln x = 0

lnx=1\ln x = 1

x=ex = e

Step 3: Evaluate the function at the critical points and endpoints

We now evaluate f(x)f(x) at the critical point x=ex = e and at the endpoints of the interval [1,e2][1, e^2].

  1. At x=1x = 1: f(1)=101(2ln1)=101(20)=20f(1) = 10 \cdot 1 \cdot (2 - \ln 1) = 10 \cdot 1 \cdot (2 - 0) = 20

  2. At x=ex = e: f(e)=10e(2lne)=10e(21)=10ef(e) = 10 \cdot e \cdot (2 - \ln e) = 10 \cdot e \cdot (2 - 1) = 10e

    Since e2.718e \approx 2.718, 10e27.1810e \approx 27.18.

  3. At x=e2x = e^2: f(e2)=10e2(2lne2)=10e2(22)=0f(e^2) = 10 \cdot e^2 \cdot (2 - \ln e^2) = 10 \cdot e^2 \cdot (2 - 2) = 0

Step 4: Determine the absolute minimum

Among the values computed:

  • f(1)=20f(1) = 20
  • f(e)27.18f(e) \approx 27.18
  • f(e2)=0f(e^2) = 0

The absolute minimum value of f(x)f(x) on the interval [1,e2][1, e^2] is 0 at x=e2x = e^2.

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Math Problem Analysis

Mathematical Concepts

Calculus
Optimization

Formulas

Derivative formula
Critical points evaluation

Theorems

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Suitable Grade Level

Advanced High School