Find the area of the surface obtained by rotating the curve about the x-axis. X 름-빨 In x Select the correct answer. y = [1,720-81 In (7) - (In (7))² [359-361 n (7) - (In(7))²] [648-491n (7) - (In(7))²] [2,599-1001n (7) - (In(7))²] 1 ≤ x ≤7 7 2

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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### Surface Area of a Rotated Curve

To find the area of the surface obtained by rotating the curve about the x-axis, consider the curve defined by the equation:
\[ y = \frac{x^2}{4} - \frac{\ln x}{2}, \quad 1 \leq x \leq 7 \]

#### Question:
Select the correct answer for the area obtained by rotating the given curve about the x-axis.

The options are:
1. \(\frac{\pi}{4} \left[ 1,720 - 81 \ln (7) - (\ln (7))^2 \right]\)
2. \(\frac{\pi}{4} \left[ 359 - 36 \ln (7) - (\ln (7))^2 \right]\)
3. \(\frac{\pi}{4} \left[ 648 - 49 \ln (7) - (\ln (7))^2 \right]\)
4. \(\frac{\pi}{4} \left[ 2,599 - 100 \ln (7) - (\ln (7))^2 \right]\)

To solve this problem, we need to determine the correct expression for the area of the surface generated by rotating the given curve \( y = \frac{x^2}{4} - \frac{\ln x}{2} \) around the x-axis between \( x = 1 \) and \( x = 7 \).

### Explanation:
In solving problems of this type, we typically apply the formula for the surface area of a solid of revolution around the x-axis, given by:
\[ A = 2\pi \int_a^b y \sqrt{1 + \left(\frac{dy}{dx}\right)^2} \, dx \]

Where:
- \( y \) is the function describing the curve.
- \( \frac{dy}{dx} \) is the derivative of the function describing the curve.
- \( [a, b] \) is the interval over which we are integrating.

In this case:
- \( a = 1 \)
- \( b = 7 \)
- \( y = \frac{x^2}{4} - \frac{\ln x}{2} \)

You would compute \(\frac{dy}{dx}\), plug these into the surface area formula, and evaluate the integral to obtain the correct solution.
Transcribed Image Text:### Surface Area of a Rotated Curve To find the area of the surface obtained by rotating the curve about the x-axis, consider the curve defined by the equation: \[ y = \frac{x^2}{4} - \frac{\ln x}{2}, \quad 1 \leq x \leq 7 \] #### Question: Select the correct answer for the area obtained by rotating the given curve about the x-axis. The options are: 1. \(\frac{\pi}{4} \left[ 1,720 - 81 \ln (7) - (\ln (7))^2 \right]\) 2. \(\frac{\pi}{4} \left[ 359 - 36 \ln (7) - (\ln (7))^2 \right]\) 3. \(\frac{\pi}{4} \left[ 648 - 49 \ln (7) - (\ln (7))^2 \right]\) 4. \(\frac{\pi}{4} \left[ 2,599 - 100 \ln (7) - (\ln (7))^2 \right]\) To solve this problem, we need to determine the correct expression for the area of the surface generated by rotating the given curve \( y = \frac{x^2}{4} - \frac{\ln x}{2} \) around the x-axis between \( x = 1 \) and \( x = 7 \). ### Explanation: In solving problems of this type, we typically apply the formula for the surface area of a solid of revolution around the x-axis, given by: \[ A = 2\pi \int_a^b y \sqrt{1 + \left(\frac{dy}{dx}\right)^2} \, dx \] Where: - \( y \) is the function describing the curve. - \( \frac{dy}{dx} \) is the derivative of the function describing the curve. - \( [a, b] \) is the interval over which we are integrating. In this case: - \( a = 1 \) - \( b = 7 \) - \( y = \frac{x^2}{4} - \frac{\ln x}{2} \) You would compute \(\frac{dy}{dx}\), plug these into the surface area formula, and evaluate the integral to obtain the correct solution.
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