Convergence Tests for Series of Real Numbers

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Questions and Answers

If a series ∑an converges, which of the following statements is true about the sequence of terms {an}?

  • The sequence of terms {an} diverges to ∞.
  • The sequence of terms {an} converges to 0. (correct)
  • The sequence of terms {an} converges to 1.
  • The sequence of terms {an} oscillates.

What is the sum of a convergent geometric series ∑ar^(n-1)?

  • a/(1 - r) (correct)
  • a*r
  • a/(1 + r)
  • a/r

If a p-series ∑(1/n^p) converges, what can be said about the value of p?

  • p < 1
  • p = 1
  • p ≤ 0
  • p > 1 (correct)

If 0 ≤ an ≤ bn for all n, and ∑bn diverges, what can be said about the convergence of ∑an?

<p>The series ∑an diverges. (C)</p> Signup and view all the answers

If lim (an / bn) = L, where 0 < L < ∞, what can be said about the convergence of ∑an and ∑bn?

<p>Both ∑an and ∑bn converge or both diverge. (C)</p> Signup and view all the answers

If lim (|an+1 / an|) = L, where L = 1, what can be said about the convergence of the series ∑an?

<p>The ratio test is inconclusive. (D)</p> Signup and view all the answers

If lim (|an|^(1/n)) = L, where L = 1, what can be said about the convergence of the series ∑an?

<p>The root test is inconclusive. (B)</p> Signup and view all the answers

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Study Notes

Convergence Tests for Series of Real Numbers

Nth Term Test

  • If the sequence of terms {an} converges to 0, then the series ∑an converges.
  • If the sequence of terms {an} does not converge to 0, then the series ∑an diverges.

Geometric Series Test

  • A geometric series ∑ar^(n-1) converges if |r| < 1 and diverges if |r| ≥ 1.
  • The sum of a convergent geometric series is a/(1 - r).

p-Series Test

  • A p-series ∑(1/n^p) converges if p > 1 and diverges if p ≤ 1.

Comparison Test

  • If 0 ≤ an ≤ bn for all n, and ∑bn converges, then ∑an converges.
  • If an ≥ bn for all n, and ∑bn diverges, then ∑an diverges.

Limit Comparison Test

  • If lim (an / bn) = L, where 0 < L < ∞, then ∑an and ∑bn both converge or both diverge.

Ratio Test

  • If lim (|an+1 / an|) = L, then:
    • If L < 1, the series ∑an converges.
    • If L > 1, the series ∑an diverges.
    • If L = 1, the test is inconclusive.

Root Test

  • If lim (|an|^(1/n)) = L, then:
    • If L < 1, the series ∑an converges.
    • If L > 1, the series ∑an diverges.
    • If L = 1, the test is inconclusive.

These convergence tests can be used to determine whether a series of real numbers converges or diverges.

Convergence Tests for Series of Real Numbers

Nth Term Test

  • Necessary condition for series convergence: sequence of terms {an} converges to 0
  • Sufficient condition for series divergence: sequence of terms {an} does not converge to 0

Geometric Series Test

  • Convergence condition: |r| < 1
  • Divergence condition: |r| ≥ 1
  • Sum of a convergent geometric series: a/(1 - r)

p-Series Test

  • Convergence condition: p > 1
  • Divergence condition: p ≤ 1

Comparison Test

  • Convergence condition: 0 ≤ an ≤ bn for all n, and ∑bn converges
  • Divergence condition: an ≥ bn for all n, and ∑bn diverges

Limit Comparison Test

  • Convergence/divergence condition: lim (an / bn) = L, where 0 < L < ∞

Ratio Test

  • Convergence condition: lim (|an+1 / an|) < 1
  • Divergence condition: lim (|an+1 / an|) > 1
  • Inconclusive condition: lim (|an+1 / an|) = 1

Root Test

  • Convergence condition: lim (|an|^(1/n)) < 1
  • Divergence condition: lim (|an|^(1/n)) > 1
  • Inconclusive condition: lim (|an|^(1/n)) = 1

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