A farmer wants to fence a rectangular area of 392 square feet next to a river. Find the length and width of the rectangle which uses the least amount of fencing if no fencing is needed along the river. Assume the length of the fence runs parallel to the river. Length: Number feet Width: Number feet

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Author:James Stewart
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Chapter1: Functions And Models
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A farmer wants to fence a rectangular area of 392 square feet next to a river. Find the length and width of the rectangle which uses the least amount of fencing if no fencing is needed along the river. Assume the length of the fence runs parallel to the river. 

### Problem Statement

A farmer wants to fence a rectangular area of 392 square feet next to a river. Find the length and width of the rectangle which uses the least amount of fencing if no fencing is needed along the river. Assume the length of the fence runs parallel to the river.

### Inputs

- **Length:** 
  - **Type:** Number
  - **Unit:** feet
  
- **Width:** 
  - **Type:** Number
  - **Unit:** feet

### Explanation

To minimize the amount of fencing required:

1. Let \( L \) be the length along the river and \( W \) be the width perpendicular to the river.
2. The area (\( A \)) is given by the formula \( L \times W = 392 \) square feet.
3. Since no fencing is required along the river, the total length of fencing required will be \( L + 2W \).

### Calculation Steps

1. Express \( L \) in terms of \( W \) using the area constraint:
   \[
   L = \frac{392}{W}
   \]

2. Substitute this into the fencing equation to minimize the function:
   \[
   F = \frac{392}{W} + 2W
   \]

3. Differentiate \( F \) with respect to \( W \) to find the critical points:
   \[
   F'(W) = -\frac{392}{W^2} + 2
   \]

4. Solve for \( W \) when \( F'(W) = 0 \):
   \[
   -\frac{392}{W^2} + 2 = 0
   \]
   \[
   \frac{392}{W^2} = 2
   \]
   \[
   W^2 = \frac{392}{2} = 196
   \]
   \[
   W = \sqrt{196} = 14
   \]

5. Substitute \( W = 14 \) back to find \( L \):
   \[
   L = \frac{392}{14} = 28
   \]

### Conclusion

To minimize the amount of fencing required:
- **Length:** 28 feet
- **Width:** 14 feet

This results in the minimum fencing needed while maintaining the total area of 392 square feet.
Transcribed Image Text:### Problem Statement A farmer wants to fence a rectangular area of 392 square feet next to a river. Find the length and width of the rectangle which uses the least amount of fencing if no fencing is needed along the river. Assume the length of the fence runs parallel to the river. ### Inputs - **Length:** - **Type:** Number - **Unit:** feet - **Width:** - **Type:** Number - **Unit:** feet ### Explanation To minimize the amount of fencing required: 1. Let \( L \) be the length along the river and \( W \) be the width perpendicular to the river. 2. The area (\( A \)) is given by the formula \( L \times W = 392 \) square feet. 3. Since no fencing is required along the river, the total length of fencing required will be \( L + 2W \). ### Calculation Steps 1. Express \( L \) in terms of \( W \) using the area constraint: \[ L = \frac{392}{W} \] 2. Substitute this into the fencing equation to minimize the function: \[ F = \frac{392}{W} + 2W \] 3. Differentiate \( F \) with respect to \( W \) to find the critical points: \[ F'(W) = -\frac{392}{W^2} + 2 \] 4. Solve for \( W \) when \( F'(W) = 0 \): \[ -\frac{392}{W^2} + 2 = 0 \] \[ \frac{392}{W^2} = 2 \] \[ W^2 = \frac{392}{2} = 196 \] \[ W = \sqrt{196} = 14 \] 5. Substitute \( W = 14 \) back to find \( L \): \[ L = \frac{392}{14} = 28 \] ### Conclusion To minimize the amount of fencing required: - **Length:** 28 feet - **Width:** 14 feet This results in the minimum fencing needed while maintaining the total area of 392 square feet.
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