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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.9c

Volumes
Find the volume of the solid generated by revolving the region bounded on the left by the parabola x = y² + 1 and on the right by the line x = 5 about
c. the line x = 5

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1
First, identify the region bounded by the curves: the parabola given by \(x = y^{2} + 1\) on the left and the vertical line \(x = 5\) on the right. Determine the range of \(y\) by finding the points where these two curves intersect. Set \(y^{2} + 1 = 5\) and solve for \(y\).
Since the solid is generated by revolving the region about the line \(x = 5\), consider the method of cylindrical shells or washers. Here, the axis of rotation is vertical, so using the shell method with respect to \(y\) is convenient.
For the shell method, the radius of a shell at a given \(y\) is the distance from the line \(x = 5\) to the shell, which is \(5 - x\). Since \(x\) varies from \(x = y^{2} + 1\) to \(x = 5\), the shell radius is \(5 - y^{2} - 1 = 4 - y^{2}\). The height of the shell is the vertical thickness, which corresponds to the difference in \(x\) values, but since we revolve around \(x=5\), the height is the length along \(x\) between the parabola and the line, which is \(5 - (y^{2} + 1) = 4 - y^{2}\).
Set up the volume integral using the shell method formula: \(V = 2\pi \int_{a}^{b} (\text{radius})(\text{height}) \, dy\). Here, the radius is the distance from the axis of rotation to the shell, and the height is the length of the shell. Determine the limits of integration \(a\) and \(b\) from the intersection points found in step 1.
Write the integral explicitly as \(V = 2\pi \int_{-c}^{c} (\text{radius})(\text{height}) \, dy\), where \(c\) is the positive \(y\)-value of the intersection. Substitute the expressions for radius and height, simplify the integrand, and prepare to evaluate the integral to find the volume.

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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

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 parallel to the slices. The volume is found by integrating 2π(radius)(height) with respect to the variable of integration.
추천 영상:
07:33
Euler's Method

Setting up the Limits of Integration and Radius/Height Expressions

Correctly identifying the bounds of the region and expressing the radius and height of shells or washers in terms of the variable of integration is crucial. For the given parabola and line, determining y-limits and expressing distances from the axis of rotation ensures accurate integral setup.
추천 영상:
가이드 코스
05:43
Definition of the Definite Integral