Abox of volume 60m3 with a squan botHom and no top IS constructd out of 2 diffennt materi als. The makerial for the botHom costs $40/m². The makri al for the sides costs $30/m? And the dimensions that minimalize total cost. (don't forget to Show that answer is a minimum) Leare answer exact or qire approximahon to 2 decimal places.

Algebra for College Students
10th Edition
ISBN:9781285195780
Author:Jerome E. Kaufmann, Karen L. Schwitters
Publisher:Jerome E. Kaufmann, Karen L. Schwitters
Chapter9: Polynomial And Rational Functions
Section9.4: Graphing Polynomial Functions
Problem 43PS
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### Problem Statement

A box of volume \(60 \, \text{m}^3\) with a square bottom and no top is constructed out of 2 different materials. The material for the bottom costs \( \$40/\text{m}^2 \). The material for the sides costs \( \$30/\text{m}^2 \).

Find the dimensions that minimize total cost. (Don't forget to show that your answer is a minimum). Leave answer exact or give approximation to 2 decimal places.

### Explanation

- **Volume of the Box:** \( V = 60 \, \text{m}^3 \)
- **Cost per Unit Area for Bottom Material:** \( \$40/\text{m}^2 \)
- **Cost per Unit Area for Side Material:** \( \$30/\text{m}^2 \)

### Step-by-Step Solution

1. **Determine the Variables:**
   - Let \( x \) be the length of one side of the square base.
   - Let \( h \) be the height of the box.

2. **Establish the Volume Constraint:**
   - Volume: \( x^2 h = 60 \Rightarrow h = \frac{60}{x^2} \)

3. **Calculate the Surface Area:**
   - Bottom area: \( x^2 \)
   - Side area: \( 4xh \)

4. **Express Total Cost:**
   - Cost for bottom: \( 40x^2 \)
   - Cost for sides: \( 30 \cdot 4xh = 120xh \)
   - Substitute for \( h \): \( 120x \left( \frac{60}{x^2} \right) = \frac{7200}{x} \)
   - Total cost: \( C(x) = 40x^2 + \frac{7200}{x} \)

5. **Find the Minimum Cost:**
   - Derive the cost function with respect to \( x \): \( C'(x) = 80x - \frac{7200}{x^2} \)
   - Set the derivative to zero to find critical points: \( 80x - \frac{7200}{x^2} = 0 \Rightarrow 80x^3 = 7200 \Rightarrow x^3 = 90 \Rightarrow x = \sqrt
Transcribed Image Text:### Problem Statement A box of volume \(60 \, \text{m}^3\) with a square bottom and no top is constructed out of 2 different materials. The material for the bottom costs \( \$40/\text{m}^2 \). The material for the sides costs \( \$30/\text{m}^2 \). Find the dimensions that minimize total cost. (Don't forget to show that your answer is a minimum). Leave answer exact or give approximation to 2 decimal places. ### Explanation - **Volume of the Box:** \( V = 60 \, \text{m}^3 \) - **Cost per Unit Area for Bottom Material:** \( \$40/\text{m}^2 \) - **Cost per Unit Area for Side Material:** \( \$30/\text{m}^2 \) ### Step-by-Step Solution 1. **Determine the Variables:** - Let \( x \) be the length of one side of the square base. - Let \( h \) be the height of the box. 2. **Establish the Volume Constraint:** - Volume: \( x^2 h = 60 \Rightarrow h = \frac{60}{x^2} \) 3. **Calculate the Surface Area:** - Bottom area: \( x^2 \) - Side area: \( 4xh \) 4. **Express Total Cost:** - Cost for bottom: \( 40x^2 \) - Cost for sides: \( 30 \cdot 4xh = 120xh \) - Substitute for \( h \): \( 120x \left( \frac{60}{x^2} \right) = \frac{7200}{x} \) - Total cost: \( C(x) = 40x^2 + \frac{7200}{x} \) 5. **Find the Minimum Cost:** - Derive the cost function with respect to \( x \): \( C'(x) = 80x - \frac{7200}{x^2} \) - Set the derivative to zero to find critical points: \( 80x - \frac{7200}{x^2} = 0 \Rightarrow 80x^3 = 7200 \Rightarrow x^3 = 90 \Rightarrow x = \sqrt
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