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Ch. 8 - Techniques of Integration
Hass - Thomas' Calculus 15th Edition
Hass15th EditionThomas' CalculusISBN: 9780137616077Not the one you use?Change textbook
Chapter 8, Problem 8.8.36

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 -1 to 1 of (dθ / (θ² - 2θ))

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1
First, identify the integrand and the interval of integration. The integral is \( \int_{-1}^{1} \frac{d\theta}{\theta^{2} - 2\theta} \). Notice that the denominator can be factored as \( \theta(\theta - 2) \).
Check for points where the integrand is undefined or discontinuous within the interval \([-1, 1]\). Since the denominator is zero when \( \theta = 0 \) or \( \theta = 2 \), and \( 0 \) lies within the interval, the integral is improper at \( \theta = 0 \).
Split the integral at the point of discontinuity to handle the improper integral properly: \( \int_{-1}^{1} \frac{d\theta}{\theta(\theta - 2)} = \int_{-1}^{0} \frac{d\theta}{\theta(\theta - 2)} + \int_{0}^{1} \frac{d\theta}{\theta(\theta - 2)} \).
To test for convergence, analyze the behavior of the integrand near \( \theta = 0 \). Compare \( \frac{1}{\theta(\theta - 2)} \) near zero to a simpler function that dominates or is dominated by it, such as \( \frac{1}{\theta} \), since near zero \( \theta - 2 \) is approximately \(-2\), a constant.
Use the Direct Comparison Test or Limit Comparison Test with the simpler function \( \frac{1}{|\theta|} \) on each side of zero to determine if the improper integral converges or diverges near \( \theta = 0 \).

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Key Concepts

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

Improper Integrals and Convergence

An improper integral involves integrands with discontinuities or infinite limits. To determine convergence, we analyze the behavior near points where the function is undefined or infinite, such as singularities within the interval. If the integral's limit exists finitely, the integral converges; otherwise, it diverges.
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Direct Comparison Test

The Direct Comparison Test compares the given integral's 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 careful choice of comparison functions.
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Limit Comparison Test

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