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Ch. 5 - Integrals
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077당신이 사용하는 게 아니라요?교과서 변경
5장, 문제 5.PE.45

Evaluate the integrals in Exercises 37–46.


∫(sin 2θ - cos 2θ)/(sin 2θ + cos 2θ)³dθ

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Start by examining the integral \( \int \frac{\sin 2\theta - \cos 2\theta}{(\sin 2\theta + \cos 2\theta)^3} \, d\theta \). Notice that the numerator and denominator involve \( \sin 2\theta + \cos 2\theta \) and its derivative might be related to the numerator.
Set \( u = \sin 2\theta + \cos 2\theta \). Then, compute \( \frac{du}{d\theta} \) to find the differential \( du \). Since \( \frac{d}{d\theta}(\sin 2\theta) = 2\cos 2\theta \) and \( \frac{d}{d\theta}(\cos 2\theta) = -2\sin 2\theta \), we get \( \frac{du}{d\theta} = 2\cos 2\theta - 2\sin 2\theta = 2(\cos 2\theta - \sin 2\theta) \).
Rewrite the numerator \( \sin 2\theta - \cos 2\theta \) in terms of \( \cos 2\theta - \sin 2\theta \) to relate it to \( du/d\theta \). Notice that \( \sin 2\theta - \cos 2\theta = - (\cos 2\theta - \sin 2\theta) \).
Express the integral in terms of \( u \) and \( du \) by substituting the numerator and denominator accordingly. The integral becomes \( \int \frac{- (\cos 2\theta - \sin 2\theta)}{u^3} \, d\theta \). Using the expression for \( du \), solve for \( d\theta \) and substitute into the integral.
Simplify the integral to a function of \( u \) and \( du \), which should be easier to integrate. After integration, substitute back \( u = \sin 2\theta + \cos 2\theta \) to express the answer in terms of \( \theta \).

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Trigonometric Identities

Trigonometric identities are equations involving trigonometric functions that hold true for all values within their domains. They help simplify expressions, such as rewriting sin 2θ and cos 2θ in terms of other functions or combining terms. Recognizing and applying these identities is essential to simplify the integral's numerator and denominator.
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Verifying Trig Equations as Identities

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The substitution method involves changing variables to simplify an integral. By letting a new variable represent a function inside the integral (e.g., u = sin 2θ + cos 2θ), the integral can be transformed into a more manageable form. This technique is crucial for integrals where the derivative of the substitution appears elsewhere in the integrand.
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Euler's Method

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Integration of rational functions involves integrating ratios of polynomials or expressions raised to powers. When the integrand is a rational function of trigonometric expressions, rewriting it and using substitution can reduce it to a standard form. Understanding how to handle powers in the denominator and simplify the integrand is key to solving such integrals.
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