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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 8.2.68

In Exercises 67–73, use integration by parts to establish the reduction formula.
∫ x^n sin(x) dx = -x^n cos(x) + n ∫ x^(n-1) cos(x) dx

Guida verificata passo dopo passo
1
Identify the parts for integration by parts: let \(u = x^n\) and \(dv = \sin(x) \, dx\).
Compute the derivatives and integrals needed: \(du = n x^{n-1} \, dx\) and \(v = -\cos(x)\) (since \(\frac{d}{dx}(-\cos(x)) = \sin(x)\)).
Apply the integration by parts formula: \(\int u \, dv = uv - \int v \, du\), which gives \(\int x^n \sin(x) \, dx = -x^n \cos(x) - \int (-\cos(x)) (n x^{n-1}) \, dx\).
Simplify the integral expression: \(-x^n \cos(x) + n \int x^{n-1} \cos(x) \, dx\).
This establishes the reduction formula: \(\int x^n \sin(x) \, dx = -x^n \cos(x) + n \int x^{n-1} \cos(x) \, dx\).

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Integration by Parts

Integration by parts is a technique derived from the product rule of differentiation. It transforms the integral of a product of functions into simpler integrals, using the formula ∫u dv = uv - ∫v du. Choosing u and dv appropriately is crucial to simplify the integral effectively.
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A reduction formula expresses an integral involving a parameter (like n) in terms of a similar integral with a lower parameter value. It helps solve integrals recursively by breaking them down step-by-step, making complex integrals manageable through repeated application.
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