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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 8.8.22

The integrals in Exercises 1–34 converge. Evaluate the integrals without using tables.
∫₀^∞ 2e^(−θ) sinθ dθ

Guida verificata passo dopo passo
1
Recognize that the integral is of the form \(\int_0^{\infty} e^{-a\theta} \sin(b\theta) \, d\theta\) where \(a = 1\) and \(b = 1\), but here the integrand is \(2 e^{-\theta} \sin \theta\). Factor out the constant 2 to write the integral as \(2 \int_0^{\infty} e^{-\theta} \sin \theta \, d\theta\).
Recall the standard formula for the integral \(\int_0^{\infty} e^{-p x} \sin(q x) \, dx = \frac{q}{p^2 + q^2}\), valid for \(p > 0\). Here, identify \(p = 1\) and \(q = 1\).
Apply the formula to evaluate \(\int_0^{\infty} e^{-\theta} \sin \theta \, d\theta = \frac{1}{1^2 + 1^2} = \frac{1}{2}\).
Multiply the result by the constant factor 2 that was factored out initially, so the original integral becomes \(2 \times \frac{1}{2}\).
Conclude that the value of the integral is the product found in the previous step, which completes the evaluation without using tables.

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