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Ch. 6 - Applications of Definite Integrals
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077당신이 사용하는 게 아니라요?교과서 변경
6장, 문제 6.PE.8c

Volumes
Find the volume of the solid generated by revolving the “triangular” region bounded by the curve y = 4/x³ and the lines x = 1 and y = 1/2 about
c. the line x = 2

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1
First, identify the region bounded by the curve \(y = \frac{4}{x^3}\), the vertical line \(x = 1\), and the horizontal line \(y = \frac{1}{2}\). Determine the other boundary for \(x\) by solving \(\frac{4}{x^3} = \frac{1}{2}\) to find the \(x\)-value where the curve meets \(y = \frac{1}{2}\).
Since the solid is generated by revolving the region about the vertical line \(x = 2\), use the method of cylindrical shells. The formula for the volume using shells is \(V = 2\pi \int_a^b (\text{radius})(\text{height}) \, dx\).
Express the radius of a typical shell as the distance from the shell at position \(x\) to the axis of rotation \(x = 2\). This radius is \(r = 2 - x\) because the shells are vertical slices between \(x=1\) and the \(x\)-value found in step 1.
The height of each shell is the vertical distance between the curve and the line \(y = \frac{1}{2}\). Since the region is bounded above by \(y = \frac{4}{x^3}\) and below by \(y = \frac{1}{2}\), the height is \(h = \frac{4}{x^3} - \frac{1}{2}\).
Set up the integral for the volume as \(V = 2\pi \int_{1}^{x_0} (2 - x) \left( \frac{4}{x^3} - \frac{1}{2} \right) dx\), where \(x_0\) is the \(x\)-value found in step 1. This integral represents the volume of the solid generated by revolving the region about \(x=2\).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Volume of Solids of Revolution

This concept involves finding the volume of a 3D solid formed by rotating a 2D region around a given axis. Methods like the disk, washer, or shell method are used depending on the axis and shape. Understanding how to set up integrals to represent these volumes is essential.
추천 영상:
04:48
Finding Volume Using Disks

Shell Method for Volumes

The shell method calculates volume by integrating cylindrical shells formed by revolving vertical or horizontal slices around an axis. It is especially useful when the axis of rotation is vertical and not the y-axis, such as x = 2. The volume is found by integrating 2π(radius)(height) dx or dy.
추천 영상:
04:48
Finding Volume Using Disks

Setting up Limits and Functions for Integration

Correctly identifying the bounds of integration and expressing the radius and height of shells or washers in terms of the variable of integration is crucial. Here, the region is bounded by y = 4/x³, x = 1, and y = 1/2, so understanding how to translate these into limits and expressions relative to the axis x = 2 is key.
추천 영상:
06:11
Limits of Rational Functions: Denominator = 0