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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 8.1.14

The integrals in Exercises 1–44 are in no particular order. Evaluate each integral using any algebraic method, trigonometric identity, or substitution you think is appropriate.
∫ (csc t sin 3t dt)

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Start by rewriting the integral \( \int \csc t \sin 3t \, dt \) to understand the integrand better. Recall that \( \csc t = \frac{1}{\sin t} \), so the integrand becomes \( \frac{\sin 3t}{\sin t} \).
Use the trigonometric identity for \( \sin 3t \), which is \( \sin 3t = 3 \sin t - 4 \sin^3 t \). Substitute this into the integrand to get \( \frac{3 \sin t - 4 \sin^3 t}{\sin t} \).
Simplify the fraction by dividing each term in the numerator by \( \sin t \), resulting in \( 3 - 4 \sin^2 t \). Now the integral becomes \( \int (3 - 4 \sin^2 t) \, dt \).
Recall the Pythagorean identity \( \sin^2 t = \frac{1 - \cos 2t}{2} \). Substitute this into the integral to express everything in terms of cosine: \( \int \left(3 - 4 \cdot \frac{1 - \cos 2t}{2} \right) dt \).
Simplify the integrand and then integrate term-by-term. This will involve integrating constants and cosine functions, which are straightforward to handle.

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Trigonometric Identities

Trigonometric identities are equations involving trigonometric functions that hold true for all values within their domains. They simplify expressions and integrals by rewriting complex trigonometric terms into more manageable forms, such as expressing sin(3t) using angle addition formulas.
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Integration Techniques

Integration techniques include methods like substitution, integration by parts, and algebraic manipulation. Choosing the right technique helps transform the integral into a simpler form that can be directly integrated, especially when dealing with products of trigonometric functions.
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Properties of Cosecant and Sine Functions

Understanding the properties of cosecant (csc t = 1/sin t) and sine functions is essential to simplify the integrand. Recognizing how these functions interact allows for algebraic simplification, such as canceling terms or rewriting the integrand to facilitate integration.
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Properties of Functions