(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...
icon
Related questions
Question
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.
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.
Expert Solution
steps

Step by step

Solved in 4 steps

Blurred answer
Recommended textbooks for you
Calculus: Early Transcendentals
Calculus: Early Transcendentals
Calculus
ISBN:
9781285741550
Author:
James Stewart
Publisher:
Cengage Learning
Thomas' Calculus (14th Edition)
Thomas' Calculus (14th Edition)
Calculus
ISBN:
9780134438986
Author:
Joel R. Hass, Christopher E. Heil, Maurice D. Weir
Publisher:
PEARSON
Calculus: Early Transcendentals (3rd Edition)
Calculus: Early Transcendentals (3rd Edition)
Calculus
ISBN:
9780134763644
Author:
William L. Briggs, Lyle Cochran, Bernard Gillett, Eric Schulz
Publisher:
PEARSON
Calculus: Early Transcendentals
Calculus: Early Transcendentals
Calculus
ISBN:
9781319050740
Author:
Jon Rogawski, Colin Adams, Robert Franzosa
Publisher:
W. H. Freeman
Precalculus
Precalculus
Calculus
ISBN:
9780135189405
Author:
Michael Sullivan
Publisher:
PEARSON
Calculus: Early Transcendental Functions
Calculus: Early Transcendental Functions
Calculus
ISBN:
9781337552516
Author:
Ron Larson, Bruce H. Edwards
Publisher:
Cengage Learning