Skip to main content
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 8.3.4

Evaluate the integrals in Exercises 1–22.
∫ sin⁴(2x) cos(2x) dx

Guida verificata passo dopo passo
1
Recognize that the integral involves powers of sine and cosine functions with the same argument, specifically \(\sin^4(2x)\) and \(\cos(2x)\). This suggests using a substitution related to the inner function of sine and cosine.
Let \(u = \sin(2x)\). Then, compute the differential \(du\): since \(\frac{d}{dx} \sin(2x) = 2 \cos(2x)\), it follows that \(du = 2 \cos(2x) \, dx\), or equivalently, \(\cos(2x) \, dx = \frac{du}{2}\).
Rewrite the integral in terms of \(u\) using the substitution: \(\int \sin^4(2x) \cos(2x) \, dx = \int u^4 \cdot \cos(2x) \, dx = \int u^4 \cdot \frac{du}{2} = \frac{1}{2} \int u^4 \, du\).
Integrate \(\frac{1}{2} \int u^4 \, du\) by applying the power rule for integration: \(\int u^n \, du = \frac{u^{n+1}}{n+1} + C\). So, \(\frac{1}{2} \int u^4 \, du = \frac{1}{2} \cdot \frac{u^5}{5} + C\).
Finally, substitute back \(u = \sin(2x)\) to express the answer in terms of \(x\): the integral becomes \(\frac{1}{10} \sin^5(2x) + C\).

Risposta video verificata per un problema simile:

Questa soluzione video è stata consigliata dai nostri tutor come utile per risolvere questo problema.
Durata del video:
1m

Concetti chiave

Ecco i concetti essenziali che devi comprendere per rispondere correttamente alla domanda.

Trigonometric Integration

Trigonometric integration involves techniques to integrate functions containing trigonometric expressions. It often requires using identities or substitutions to simplify powers or products of sine and cosine functions for easier integration.
Video consigliato:
Percorso guidato
6:04
Introduction to Trigonometric Functions

Substitution Method

The substitution method simplifies integrals by changing variables. For integrals like ∫sin⁴(2x)cos(2x) dx, letting u = sin(2x) transforms the integral into a polynomial form in u, making it straightforward to integrate.
Video consigliato:
07:33
Euler's Method

Power Reduction and Algebraic Manipulation

When integrating powers of trigonometric functions, expressing them in terms of lower powers or using algebraic manipulation helps. Recognizing that cos(2x) dx relates to the derivative of sin(2x) allows rewriting the integral in a simpler form.
Video consigliato:
05:58
Intro to Power Series