(5) It costs $8,000/km to lay pipe under the water and $5,000/km to walay pipe under the ground. Find the baut P that minimizes the cast of -4km- A
(5) It costs $8,000/km to lay pipe under the water and $5,000/km to walay pipe under the ground. Find the baut P that minimizes the cast of -4km- A
Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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The top one is the question, the middle one is how I solved it, and the bottom is how my professor solved it. I’m not sure why my answer is wrong and I’m confused about how my professor solved it.
![### Optimization Problem: Minimizing Cost of Laying Pipe
#### Problem Description
You need to lay a pipe from point A to point B. The setup is as follows:
- The direct horizontal distance between point A and point Q is 4 km.
- The vertical distance from point Q to point B is 20 km.
- The pipe can be laid underwater at a cost of $8,000 per kilometer or underground at a cost of $5,000 per kilometer.
- The goal is to find the point P on line AQ that minimizes the total cost of laying the pipe from A to B.
#### Diagram Explanation
A diagram illustrates the configuration with:
- Point A located 4 km horizontally from point Q.
- A vertical line from point Q to point B, which is 20 km long.
- A proposed point P on line AQ, such that the distance from A to Q is labeled as x km.
#### Cost Equation Derivation
The total cost \( C \) is given by the sum of the costs for laying the pipe underwater and underground:
\[
C = 8000 \times \sqrt{x^2 + 16} + 5000 \times (20 - x)
\]
Where:
- \( \sqrt{x^2 + 16} \) is the underwater distance (using the Pythagorean theorem).
- \( 20 - x \) is the underground distance.
#### Finding Minimum Cost
To find the optimal point P that minimizes the cost:
1. Differentiate the cost function \( C \) with respect to \( x \):
\[
\frac{dC}{dx} = 8000 \times \frac{x}{\sqrt{x^2 + 16}} - 5000 = 0
\]
2. Solve for \( x \):
\[
\frac{8000x}{\sqrt{x^2 + 16}} = 5000
\]
3. Simplifying the equation, solve using algebra to find \( x \):
\[
8000x = 5000\sqrt{x^2 + 16}
\]
4. Solving this equation:
\[
64x^2 = 25(x^2 + 16)
\]
\[
39x^2 = 400
\]
\[
x^2 = \frac{400}{39}
\]
\[
x \approx \sqrt{\frac{400}{39}} \approx 3.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fd8dbfa7e-a078-49e6-9bf5-3b7d38009db0%2Febdeeffe-edeb-4f30-887b-be4fcdfd376f%2Fujhxpar_processed.jpeg&w=3840&q=75)
Transcribed Image Text:### Optimization Problem: Minimizing Cost of Laying Pipe
#### Problem Description
You need to lay a pipe from point A to point B. The setup is as follows:
- The direct horizontal distance between point A and point Q is 4 km.
- The vertical distance from point Q to point B is 20 km.
- The pipe can be laid underwater at a cost of $8,000 per kilometer or underground at a cost of $5,000 per kilometer.
- The goal is to find the point P on line AQ that minimizes the total cost of laying the pipe from A to B.
#### Diagram Explanation
A diagram illustrates the configuration with:
- Point A located 4 km horizontally from point Q.
- A vertical line from point Q to point B, which is 20 km long.
- A proposed point P on line AQ, such that the distance from A to Q is labeled as x km.
#### Cost Equation Derivation
The total cost \( C \) is given by the sum of the costs for laying the pipe underwater and underground:
\[
C = 8000 \times \sqrt{x^2 + 16} + 5000 \times (20 - x)
\]
Where:
- \( \sqrt{x^2 + 16} \) is the underwater distance (using the Pythagorean theorem).
- \( 20 - x \) is the underground distance.
#### Finding Minimum Cost
To find the optimal point P that minimizes the cost:
1. Differentiate the cost function \( C \) with respect to \( x \):
\[
\frac{dC}{dx} = 8000 \times \frac{x}{\sqrt{x^2 + 16}} - 5000 = 0
\]
2. Solve for \( x \):
\[
\frac{8000x}{\sqrt{x^2 + 16}} = 5000
\]
3. Simplifying the equation, solve using algebra to find \( x \):
\[
8000x = 5000\sqrt{x^2 + 16}
\]
4. Solving this equation:
\[
64x^2 = 25(x^2 + 16)
\]
\[
39x^2 = 400
\]
\[
x^2 = \frac{400}{39}
\]
\[
x \approx \sqrt{\frac{400}{39}} \approx 3.
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