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alternating series test (Theorem)

The alternating series test, or the Leibniz's Theorem, states the following:

Theorem [1,2] Let $ (a_n)_{n=1}^\infty$ be a non-negative, non-increasing sequence or real numbers such that $ \lim_{n \rightarrow \infty} a_n = 0$. Then the infinite series $ \sum_{n=1}^\infty (-1)^{(n+1)} a_n$ converges.

This test provides a necessary and sufficient condition for the convergence of an alternating series, since if $ \sum_{n=1}^\infty b_n$ converges then $ a_n\to 0$.

Example: The series $ \sum_{k = 1}^{\infty}\frac{1}{k}$ does not converge, but the alternating series $ \sum_{k = 1}^{\infty}(-1)^{k+1}\frac{1}{k}$ converges to $ \ln(2)$.

Bibliography

1
W. Rudin, Principles of Mathematical Analysis, McGraw-Hill Inc., 1976.
2
E. Kreyszig, Advanced Engineering Mathematics, John Wiley & Sons, 1993, 7th ed.



"alternating series test" is owned by Koro. [ full author list (5) | owner history (2) ]
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See Also: alternating series

Other names:  Leibniz's theorem, Leibniz test

Attachments:
proof of alternating series test (Proof) by Wkbj79
proof of Leibniz's theorem (using Dirichlet's convergence test) (Proof) by mathcam
Leibniz' estimate for alternating series (Theorem) by pahio
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Cross-references: necessary and sufficient, converges, series, infinite, real numbers, sequence
There are 6 references to this entry.

This is version 14 of alternating series test, born on 2002-02-24, modified 2008-05-11.
Object id is 2588, canonical name is AlternatingSeriesTest.
Accessed 13873 times total.

Classification:
AMS MSC40-00 (Sequences, series, summability :: General reference works )
 40A05 (Sequences, series, summability :: Convergence and divergence of infinite limiting processes :: Convergence and divergence of series and sequences)

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