Techniques of Integration · Improper Integrals

Improper Integral: Type I (Infinite Limit)

af(x)dx=limtatf(x)dx\int_a^{\infty} f(x)\, dx = \lim_{t \to \infty} \int_a^t f(x)\, dx

When the upper (or lower) limit is infinite, replace it with a variable t and take the limit. If the limit is finite, the integral converges.

  • 0 variables
  • 2 worked examples
  • 16 in Techniques of Integration

Worked examples

Evaluate ∫₁^∞ 1/x² dx.
  1. lim(t→∞) ∫₁ᵗ x⁻² dx = lim(t→∞) [-1/x]₁ᵗ = lim(t→∞) (-1/t + 1) = 1

Answer: 1 (converges)

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Evaluate ∫₁^∞ 1/x dx.

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Practice

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