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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 8.8.46

In Exercises 35–68, use integration, the Direct Comparison Test, or the Limit Comparison Test to test the integrals for convergence. If more than one method applies, use whatever method you prefer.
∫ from 0 to 1 of (dt / (t - sin t))
(Hint: t ≥ sin t for t ≥ 0)

Guida verificata passo dopo passo
1
First, analyze the behavior of the integrand near the problematic point, which is at the lower limit t = 0, because the denominator \( t - \sin t \) approaches zero there.
Use the hint \( t \geq \sin t \) for \( t \geq 0 \) to understand that the denominator \( t - \sin t \) is non-negative and approaches zero as \( t \to 0^+ \). This suggests the integrand may have a singularity at 0.
Apply the Taylor series expansion for \( \sin t \) near 0: \( \sin t = t - \frac{t^3}{6} + O(t^5) \). Substitute this into the denominator to approximate \( t - \sin t \approx \frac{t^3}{6} \) for small \( t \).
Rewrite the integrand near 0 using this approximation: \( \frac{1}{t - \sin t} \approx \frac{1}{\frac{t^3}{6}} = \frac{6}{t^3} \). This helps to compare the given integral to a simpler integral \( \int_0^1 \frac{1}{t^3} dt \).
Use the Direct Comparison Test or Limit Comparison Test by comparing \( \frac{1}{t - \sin t} \) to \( \frac{1}{t^3} \) near 0. Since \( \int_0^1 \frac{1}{t^3} dt \) diverges, conclude about the convergence or divergence of the original integral based on this comparison.

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Improper Integrals and Convergence

An improper integral involves integration over an interval where the function is unbounded or the interval is infinite. To determine convergence, we analyze the behavior of the integrand near problematic points, such as where the denominator approaches zero. Convergence means the integral approaches a finite value.
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Direct Comparison Test

The Direct Comparison Test compares the given integrand to a simpler function whose convergence behavior is known. If the integrand is less than or equal to a convergent function, the integral converges; if it is greater than or equal to a divergent function, the integral diverges. This test requires establishing inequalities between functions.
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Limit Comparison Test

The Limit Comparison Test involves taking the limit of the ratio of the given integrand to a known benchmark function as the variable approaches a critical point. If the limit is a positive finite number, both integrals share the same convergence behavior. This test is useful when direct comparison is difficult.
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