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Ch. 4 - Applications of Derivatives
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 4, Problem 4.7.37

Finding Indefinite Integrals


In Exercises 17–56, find the most general antiderivative or indefinite integral. You may need to try a solution and then adjust your guess. Check your answers by differentiation.


∫7sin(θ/3) dθ

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1
Identify the integral to solve: \(\int 7 \sin\left(\frac{\theta}{3}\right) \, d\theta\).
Recognize that the integral involves a sine function with a linear argument \(\frac{\theta}{3}\). Use substitution to simplify the integral. Let \(u = \frac{\theta}{3}\), so that \(\theta = 3u\).
Calculate the differential \(d\theta\) in terms of \(du\): since \(\theta = 3u\), then \(d\theta = 3 \, du\).
Rewrite the integral in terms of \(u\): \(\int 7 \sin(u) \, d\theta = \int 7 \sin(u) \cdot 3 \, du = \int 21 \sin(u) \, du\).
Integrate \(21 \sin(u)\) with respect to \(u\): recall that \(\int \sin(u) \, du = -\cos(u) + C\), so the integral becomes \(-21 \cos(u) + C\). Finally, substitute back \(u = \frac{\theta}{3}\) to express the answer in terms of \(\theta\).

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Key Concepts

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

Indefinite Integral

An indefinite integral represents the most general antiderivative of a function, including a constant of integration. It reverses differentiation and is expressed without limits, showing all possible functions whose derivative matches the integrand.
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Integration of Trigonometric Functions

Integrating trigonometric functions like sine involves using known antiderivatives, such as ∫sin(ax) dx = -cos(ax)/a + C. Recognizing the inner function and applying the chain rule in reverse is essential for correct integration.
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Substitution Method

The substitution method simplifies integration by changing variables to handle composite functions. For example, setting u = θ/3 transforms the integral into a simpler form, making it easier to integrate and then revert to the original variable.
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Euler's Method