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Volumes on infinite intervals Find the volume of the described solid of revolution or state that it does not exist. The region bounded by \(f(x)=\frac{\sqrt{x}}{\sqrt[3]{x^{2}+1}}\) and the \(x\) -axis on the interval \([0, \infty)\) is revolved about the \(x\) -axis.

Short Answer

Expert verified
The volume of the solid does not exist because the integral used to calculate the volume diverges.

Step by step solution

01

Setting up the integral for the disk method

Since we are revolving around the \(x\)-axis, the height of each disk is given by \(f(x)\) and the radius is \(x\). The volume of each infinitesimally small disk is given by \(\pi(x)f(x)^2dx\). We will integrate this from \(0\) to \(\infty\) to find the total volume.
02

Write the integral for the volume

The integral for the volume is given by: $$V = \int_{0}^{\infty} \pi x\left(\frac{\sqrt{x}}{\sqrt[3]{x^{2}+1}}\right)^2 dx$$
03

Simplify the integral

Let's first simplify the integral: $$ V = \pi \int_{0}^{\infty} x\left(\frac{x}{x^2 + 1}\right) dx $$
04

Evaluate the integral

Now we need to determine whether the integral converges or diverges. We can do this by comparing the integral to the integral of a simpler function that also goes to infinity. In this case, we choose the function \(\frac{x}{x^2}\), because this function is greater than \(\frac{x}{x^2+1}\) on the interval \([1,\infty)\). Let's consider the improper integral of this function: $$ \int_{1}^{\infty} \frac{x}{x^2} dx $$ To evaluate this integral, we find: $$\lim_{b\to\infty}\int_{1}^{b} \frac{x}{x^2} dx = \lim_{b\to\infty}\int_{1}^{b} \frac{1}{x} dx$$ $$= \lim_{b\to\infty}\left[ \ln{(|x|)} \right]_{1}^{b}$$ $$= \lim_{b\to\infty}\left[\ln{(|b|)}-\ln{(|1|)}\right] = \infty$$ Since the improper integral \(\int_{1}^{\infty} \frac{x}{x^2} dx\) diverges, and it is greater than the integral \(\int_{1}^{\infty} \frac{x}{x^2+1} dx\), it implies that the original integral also diverges.
05

State the result

Since the integral for the volume of the solid of revolution diverges, we can say that the volume does not exist.

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Key Concepts

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

Disk Method
The Disk Method is a technique used in calculus to find the volume of a solid of revolution. A solid of revolution is created when a region in the plane is revolved around a line, often the x-axis or y-axis, creating a 3-dimensional object.

To understand the Disk Method, imagine slicing the solid perpendicular to the axis of rotation. Each slice is a disk (think of it as a thin, circular pancake). The volume of a disk with radius \( r \) and thickness \( \, ext{d}x \, \) is given by \( \, ext{d}V = \, \pi r^2 \, ext{d}x \, \).
  • The radius \( r \) corresponds to the function value \( f(x) \) when revolving around the x-axis.
  • The volume of the solid is then calculated by integrating the volume of these disks from the starting point to the endpoint along the axis.
In our case, this involves setting up the integral from \( 0 \) to \( \, \infty \, \) because these are the bounds of the region being revolved. The function we use, \( f(x) = \frac{\sqrt{x}}{\sqrt[3]{x^2+1}} \), determines the radius of the disks.
Volume of Revolution
The Volume of Revolution is the three-dimensional space occupied by a solid created when a 2D region in the plane is rotated around a line.

To find this volume, we often use methods such as the Disk Method and the Shell Method. These methods help in breaking down complex shapes into simpler forms so that their volumes can be computed more easily.
  • For the given exercise, using the Disk Method translates the problem into integrating over all of these thin disks from 0 to infinity.
  • This calculus approach helps us understand complex volumes that appear when revolving curves.
The integral formulated in this way represents the infinite sum of these infinitesimally small volumes of disks. Calculating this integration will give us the total volume of the solid. An important aspect of doing this is to determine whether this integral converges or diverges, which will inform us about the existence of the volume.
Convergence and Divergence
Convergence and Divergence are critical concepts when dealing with improper integrals and infinite series in calculus. These terms describe the behavior of an integral or series as its variable approaches a limit.

When solving improper integrals, we evaluate whether the integral converges (i.e., approaches a particular value) or diverges (i.e., increases indefinitely). This information tells us whether the quantity being measured, such as the solid's volume, is finite or infinite.
  • In our exercise, the integral \( \int_{0}^{\infty} \pi x\left(\frac{\sqrt{x}}{\sqrt[3]{x^2+1}}\right)^2 \, ext{d}x \) describes the volume of a solid of revolution.
  • We use comparison tests with simpler, known functions to determine if this integral converges.
  • In this case, we compared it to the simpler function \( \frac{x}{x^2} \), which is greater on the interval \( [1, \, \infty) \, \).
Since this comparison function's integral diverges, the original integral also diverges, meaning the volume of the solid described in the exercise does not exist.
Calculus
Calculus is a branch of mathematics that deals with continuous change, using derivatives and integrals. It is fundamental for solving many mathematical problems, especially those involving real-world applications like physics and engineering.

The power of calculus lies in its ability to provide methods for calculating things like areas, volumes, and rates of change. In calculus, derivatives measure how a quantity changes over time, while integrals are used to find accumulated quantities such as area under a curve or, in our case, volume of a solid.
  • In this exercise, we focus on the integral component of calculus to find the volume of a solid of revolution.
  • Improper integrals in calculus, like the one we are analyzing, require attention as they involve infinite limits or integrands with infinite discontinuities.
Understanding calculus fundamentals is essential for solving problems that involve finding areas, volumes, and other summations in a continuous setting, as seen with this volume of revolution problem.

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