The majorant/minorant criterion

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The majorant criterion says if a series in a Banach space has a convergent majorant, then it converges absolutely. My question is, what if a series in a Banach space has a convergent minorant, does it converges? Or, what if a series in a Banach space has a divergent majorant, does it diverges? Thank you for help.

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Do you understand the definitions of majorant and minorant?

In any case, the following two statements are true:

  1. Every series in a Banach space, converging or not, has a convergent minorant.
  2. Every series in a Banach space, converging or not, has a divergent majorant.

But don't just take my word for it; the proofs are extremely simple (and so I leave it as an exercise for you) and will perhaps help you see why the majorant criterion is true.