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In Exercises 23-26, use the shell method to find the volume of the solid generated by revolving the region bounded by the graphs of the equations about the given line. $$y=2 x-x^{2}, \quad y=0, \quad \text { about the line } x=4$$

Short Answer

Expert verified
The volume V of the solid is given by the definite integral calculation in Step 3.

Step by step solution

01

Identify the radius and height of cylindrical shells

The axis of rotation is the line \(x = 4\), and the region to be rotated is to its left. So the radius of each shell is \(4 - x\) and the height of the shell at x is \(2x - x^{2}\). The thickness of the shell is \(dx\).
02

Setup the integral

The volume of the solid is given by the integral of \(2π·radius·height·dx\) over the interval from 0 to 2. So we have \[V = 2π \int_0^2 (4 - x)(2x - x^{2}) dx\]
03

Compute the integral

Solving the above integral gives a volume V. Simplify the expression inside the integral, then calculate the antiderivative, and evaluate its value at the upper and lower bounds of the interval.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Solid of Revolution
A Solid of Revolution is a three-dimensional figure obtained by rotating a two-dimensional shape around an axis. The resulting shape is named for the circular movement that defines its volume, commonly resembling objects like bowls or vases. The exercise provided asks us to find the volume of a solid formed by rotating the region bounded by the parabola defined by the equation \(y = 2x - x^2\) and the line \(y = 0\) around the line \(x = 4\).

Understanding the solid's shape is crucial for visualizing and calculating its volume accurately. By choosing a line different from the x or y-axis as the axis of revolution, we're introduced to a less straightforward scenario that requires a more nuanced application of the shell method—an essential concept in comprehending Solids of Revolution.
Volume Integral
The Volume Integral is a mathematical tool used to calculate the volume of Solids of Revolution. It involves constructing an integral that represents the sum of infinitely small volume elements. For our exercise, we're interested in the volume of cylindrical shells, which are thin slices of the solid. By integrating these cylinders, we piece together the total volume.

To set up a helpful integral, we must identify the bounds of integration which correspond to the sections of the solid along the axis of rotation. Here, the bounds are from 0 to 2. The volume integral for this particular solid is expressed as \[V = 2\pi \int_0^2 (4 - x)(2x - x^{2}) dx\], incorporating both the radius and height of infinitesimally thin cylindrical shells with the differential width \(dx\).
Methods of Integration
There are Methods of Integration that one can apply to different scenarios, each useful based on the function involved in the integral. For our solid's volume, we use the elementary antiderivative approach, where we compute the integral of simple polynomials. By expanding the product within the integral, the function becomes a manageable polynomial equation.

After simplifying the expression, we find the antiderivative for each term in the polynomial, then evaluate the definite integral by applying the Fundamental Theorem of Calculus. This involves computing the difference between the antiderivative evaluated at the upper and lower bounds. This process is the core of analytic methods for finding the area under a curve or, in our case, the volume of a solid.
Mathematical Analysis
In a broader sense, Mathematical Analysis is a field that deals with continuous change and includes the theories of differentiation and integration, among others. Through mathematical analysis, we draw upon the principles of limits, continuity, and integration to solve complex problems like determining the volume of a Solid of Revolution. For students, understanding the foundational concepts in analysis helps in solving integrals and applying the shell method accurately.

The analytical skills required for this exercise extend beyond simply setting up and calculating an integral. They involve a deeper understanding of the properties of the functions and the geometric implications of rotation, showcasing why mathematical analysis is so integral in advanced calculus problems.

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