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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077당신이 사용하는 게 아니라요?교과서 변경
8장, 문제 8.6.44

Use reduction formulas to evaluate the integrals in Exercises 41–50.
∫ 2 sin^2(t) sec^4(t) dt

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Start by rewriting the integral to clearly identify the powers of trigonometric functions: \(\int 2 \sin^{2}(t) \sec^{4}(t) \, dt\).
Recall that \(\sec(t) = \frac{1}{\cos(t)}\), so \(\sec^{4}(t) = \frac{1}{\cos^{4}(t)}\). This allows rewriting the integral as \(\int 2 \sin^{2}(t) \frac{1}{\cos^{4}(t)} \, dt\).
Express \(\sin^{2}(t)\) in terms of \(\cos(t)\) using the Pythagorean identity: \(\sin^{2}(t) = 1 - \cos^{2}(t)\). Substitute this into the integral to get \(\int 2 (1 - \cos^{2}(t)) \frac{1}{\cos^{4}(t)} \, dt\).
Split the integral into two separate integrals: \(\int 2 \frac{1}{\cos^{4}(t)} \, dt - \int 2 \frac{\cos^{2}(t)}{\cos^{4}(t)} \, dt\), which simplifies to \(\int 2 \sec^{4}(t) \, dt - \int 2 \sec^{2}(t) \, dt\).
Use the reduction formulas for \(\int \sec^{n}(t) \, dt\) to evaluate each integral separately. The reduction formula for \(\int \sec^{n}(t) \, dt\) is: \(\int \sec^{n}(t) \, dt = \frac{\sec^{n-2}(t) \tan(t)}{n-1} + \frac{n-2}{n-1} \int \sec^{n-2}(t) \, dt\) for \(n > 1\). Apply this formula to \(\int \sec^{4}(t) \, dt\) and recall that \(\int \sec^{2}(t) \, dt = \tan(t) + C\).

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주요 개념

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

Reduction Formulas

Reduction formulas are recursive relations that express an integral involving a power of a function in terms of an integral with a lower power. They simplify complex integrals by breaking them down step-by-step, often used for powers of trigonometric functions.
추천 영상:
5:59
Recursive Formulas

Trigonometric Identities

Trigonometric identities, such as sin²(t) = 1 - cos²(t) and sec²(t) = 1 + tan²(t), help rewrite integrals into more manageable forms. Using these identities can simplify the integrand and make it easier to apply reduction formulas or substitution.
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Verifying Trig Equations as Identities

Integration Techniques for Trigonometric Functions

Techniques like substitution, integration by parts, and rewriting powers of sine and secant functions are essential for evaluating integrals involving trigonometric expressions. Recognizing when to apply these methods is key to solving the integral efficiently.
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Introduction to Trigonometric Functions