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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 8.8.90c

90. Consider the infinite region in the first quadrant bounded by the graphs of
y = 1 / √x, y = 0, x = 0, and x = 1.
b. Find the volume of the solid formed by revolving the region (ii) about the y-axis.

Guida verificata passo dopo passo
1
First, identify the region bounded by the curves: \( y = \frac{1}{\sqrt{x}} \), \( y = 0 \), \( x = 0 \), and \( x = 1 \). This region lies in the first quadrant between \( x = 0 \) and \( x = 1 \), above the x-axis and below the curve \( y = \frac{1}{\sqrt{x}} \).
Since the solid is formed by revolving this region about the y-axis, we will use the method of cylindrical shells. The formula for the volume using cylindrical shells when revolving around the y-axis is: \(\n\[\n\)\[ V = 2\pi \int_{a}^{b} (\text{radius})(\text{height}) \, dx \]\(\n\]\nwhere\) the radius is the distance from the y-axis (which is \( x \)) and the height is the function value \( y = \frac{1}{\sqrt{x}} \).
Set up the integral with the limits of integration from \( x = 0 \) to \( x = 1 \): \(\n\[\n\)\[ V = 2\pi \int_{0}^{1} x \cdot \frac{1}{\sqrt{x}} \, dx \]\(\n\]\nSimplify\) the integrand before integrating.
Simplify the integrand \( x \cdot \frac{1}{\sqrt{x}} = x \cdot x^{-1/2} = x^{1 - \frac{1}{2}} = x^{\frac{1}{2}} \). So the integral becomes \(\n\)\(\n\)\[ V = 2\pi \int_{0}^{1} x^{\frac{1}{2}} \, dx \]
Evaluate the integral \( \int_{0}^{1} x^{\frac{1}{2}} \, dx \) using the power rule for integration: \(\n\[\n\)\[ \int x^{n} \, dx = \frac{x^{n+1}}{n+1} + C \]\(\n\]\nApply\) the limits from 0 to 1 and multiply by \( 2\pi \) to express the volume.

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Concetti chiave

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Setting up the region bounded by curves

Understanding the region involves identifying the area enclosed by the given curves y = 1/√x, y = 0, x = 0, and x = 1 in the first quadrant. This means recognizing the limits of integration and the shape formed, which is essential before applying volume formulas.
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Method of cylindrical shells for volume

When revolving a region around the y-axis, the cylindrical shells method is often used. It involves integrating the volume of thin cylindrical shells with radius equal to the x-value, height given by the function, and thickness dx, allowing calculation of the solid's volume.
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Integration with respect to x

Since the region is bounded between x = 0 and x = 1, and the function is given as y in terms of x, the volume integral is set up with respect to x. Proper integration techniques must be applied to evaluate the integral and find the exact volume.
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