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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 8, Problem 8.3.76

Volume: Find the volume of the solid formed by revolving the region bounded by the graphs of y = sin x + sec x, y = 0, x = 0, and x = π/3 about the x-axis.

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Identify the region bounded by the curves: the upper curve is given by \(y = \sin x + \sec x\), the lower boundary is \(y = 0\), and the vertical boundaries are \(x = 0\) and \(x = \frac{\pi}{3}\).
Since the solid is formed by revolving this region about the x-axis, use the disk method to find the volume. The volume element is a disk with radius equal to the function value \(y\) at each \(x\), so the volume is given by integrating the area of these disks along the x-axis.
Write the volume integral as \(V = \pi \int_{0}^{\frac{\pi}{3}} \left( \sin x + \sec x \right)^2 \, dx\), where the integrand is the square of the radius function.
Expand the integrand \(\left( \sin x + \sec x \right)^2\) to simplify the integral before integrating. This will give \(\sin^2 x + 2 \sin x \sec x + \sec^2 x\).
Set up the integral with the expanded terms and prepare to integrate each term separately over the interval \([0, \frac{\pi}{3}]\). Remember to use appropriate trigonometric identities and integration techniques for each term.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Volume of Solids of Revolution

This concept involves finding the volume of a 3D solid formed by rotating a 2D region around an axis. The volume can be computed using methods like the disk/washer or shell method, which integrate cross-sectional areas perpendicular to the axis of rotation.
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Finding Volume Using Disks

Disk Method

The disk method calculates volume by slicing the solid into thin disks perpendicular to the axis of rotation. Each disk's volume is approximated by π(radius)^2 times thickness, and integrating these volumes over the interval gives the total volume.
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Disk Method Using y-Axis

Integration of Trigonometric and Secant Functions

Evaluating the volume requires integrating expressions involving sin x and sec x. Understanding how to integrate these functions, either directly or using substitution and identities, is essential to solving the problem accurately.
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Introduction to Trigonometric Functions