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Ch. 6 - Applications of Integration
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 6, Problema 6.6.27a

Consider the following curves on the given intervals.  


a. Write the integral that gives the area of the surface generated when the curve is revolved about the given axis. 


y=tan x , for 0≤x≤π/4; about the x-axis 

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1
Identify the formula for the surface area generated by revolving a curve about the x-axis. The surface area \( S \) is given by the integral \( S = \int_a^b 2\pi y \sqrt{1 + \left(\frac{dy}{dx}\right)^2} \, dx \), where \( y = f(x) \).
Given the curve \( y = \tan x \) on the interval \( 0 \leq x \leq \frac{\pi}{4} \), substitute \( y = \tan x \) into the formula.
Compute the derivative \( \frac{dy}{dx} = \sec^2 x \).
Substitute \( y = \tan x \) and \( \frac{dy}{dx} = \sec^2 x \) into the surface area integral to get \( S = \int_0^{\frac{\pi}{4}} 2\pi \tan x \sqrt{1 + (\sec^2 x)^2} \, dx \).
Simplify the expression inside the square root as much as possible before setting up the integral for evaluation.

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Surface Area of Revolution

The surface area generated by revolving a curve around an axis is found using an integral formula that accounts for the curve's length and distance from the axis. For a function y = f(x) revolved about the x-axis, the surface area is given by the integral of 2π times the radius (y) times the arc length element.
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Example 1: Minimizing Surface Area

Arc Length Element (ds)

The differential arc length element ds represents a small segment of the curve and is calculated as ds = √(1 + (dy/dx)^2) dx. This accounts for both horizontal and vertical changes along the curve, ensuring the surface area integral accurately measures the curved surface.
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Arc Length of Parametric Curves

Trigonometric Function Differentiation

To set up the integral, you need the derivative of y = tan x, which is sec^2 x. Understanding how to differentiate trigonometric functions is essential to find dy/dx, which is used in the arc length formula for the surface area calculation.
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Introduction to Trigonometric Functions