Alternating series test for convergence

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SUMMARY

The discussion focuses on the Alternating Series Test for convergence, specifically addressing the derivation of terms such as 1/2 and n/(n + 1) in the context of the test. Participants clarify that demonstrating the inequality an + 1 ≤ an is sufficient for proving convergence. The conversation emphasizes the importance of understanding the magnitude of sequence elements, noting that the sign of the terms does not affect this comparison. The final steps of the proof involve recognizing the difference between powers of -1 and their magnitudes.

PREREQUISITES
  • Understanding of the Alternating Series Test
  • Familiarity with sequences and series in calculus
  • Knowledge of inequalities and their applications in proofs
  • Basic grasp of limits and convergence concepts
NEXT STEPS
  • Study the formal proof of the Alternating Series Test
  • Learn about convergence tests such as the Ratio Test and Root Test
  • Explore examples of alternating series and their convergence properties
  • Review the concept of absolute convergence versus conditional convergence
USEFUL FOR

Students studying calculus, particularly those focusing on series and convergence, as well as educators looking for clarification on the Alternating Series Test methodology.

Maddie1609
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Homework Statement



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Homework Equations



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The Attempt at a Solution



I don't get how they got what's stated in the above picture. Where does 1/2 and n/(n + 1) come from? Can't you just show that an + 1 ≤ an?
 
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Maddie1609 said:
Where does 1/2 and n/(n + 1) come from? Can't you just show that an + 1 ≤ an?
That's what they do. The logic is easier to follow if you start with the result and reduce this to something true (look at the steps in reverse order), but this direction works as well. The first line is then a clever guess what will be needed later (and the statement is clearly true).
 
mfb said:
That's what they do. The logic is easier to follow if you start with the result and reduce this to something true (look at the steps in reverse order), but this direction works as well. The first line is then a clever guess what will be needed later (and the statement is clearly true).
A lot easier to follow that direction, thanks! The final step has 2n and 2n - 1 instead of (-2)n and (-2)n - 1 which I don't get.
 
The test compares the magnitude of the sequence elements only, powers of -1 don't change the magnitude.
The sign has to be checked separately (easy here).
 
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mfb said:
The test compares the magnitude of the sequence elements only, powers of -1 don't change the magnitude.
The sign has to be checked separately (easy here).
Oh okay! Thank you :smile:
 

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