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Question 17933: Conditional Convergence Needs Both Convergence and Absolute Divergence

On this page
  1. Original question and givens
  2. Definition and scope
  3. Step-by-step derivation
  4. Reverse checks
  5. Result
  6. This question review and source binding

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R0034-17933 · q-20261014-advance-20261104-r03-absolute-convergence-of-series-0033

Original question and givens

Use terms (−1)^k/(k+shift), k=0,1,..., positive shift=8, and display n=5 terms. Give (shift, n, terms, series_converges, absolutely_converges, certificate).

  • G001 — Use terms (−1)^k/(k+shift), k=0,1,..., positive shift=8, and display n=5 terms. Give (shift, n, terms, series_converges, absolutely_converges, certificate).

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

Step-by-step derivation

S001 · implies

Before

source operation=absseries-conditional-alternating;original question snapshot retained;source presentation interface resolved in this page

After

EXPLICIT ordered output fields=[shift, n, terms, series_converges, absolutely_converges, certificate]

Conditions: none

Preserve the original snapshot's historical interface marker while listing the full ordered fields here,without browser JavaScript or an external lookup.Field labels are presentation metadata,not mathematical evaluation.The fourth term-zero No marks insufficiency,not a mislabeled second convergence flag.

Step identifiers and dependencies

Rule: absseries_explicit_source_interface_fields_without_javascript · Uses: G001

S002 · calculation

Before

alternating displayed term0 denominator := sum(0, 8)

After

alternating displayed term0 denominator = 8

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

alternating displayed term0 signed value := div(1, 8)

After

alternating displayed term0 signed value = 1/8

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

alternating displayed term1 denominator := sum(1, 8)

After

alternating displayed term1 denominator = 9

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · calculation

Before

alternating displayed term1 signed value := div(-1, 9)

After

alternating displayed term1 signed value = -1/9

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · calculation

Before

alternating displayed term2 denominator := sum(2, 8)

After

alternating displayed term2 denominator = 10

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

alternating displayed term2 signed value := div(1, 10)

After

alternating displayed term2 signed value = 1/10

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · calculation

Before

alternating displayed term3 denominator := sum(3, 8)

After

alternating displayed term3 denominator = 11

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S007

S009 · calculation

Before

alternating displayed term3 signed value := div(-1, 11)

After

alternating displayed term3 signed value = -1/11

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · calculation

Before

alternating displayed term4 denominator := sum(4, 8)

After

alternating displayed term4 denominator = 12

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S009

S011 · calculation

Before

alternating displayed term4 signed value := div(1, 12)

After

alternating displayed term4 signed value = 1/12

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S010

S012 · implies

Before

absolute series of declared alternating tail:DECLARED whole positive tail b_k=1/(k+8),k>=0;shift>0

After

b_k decreases to0:for ANY epsilon>0 choose N with N+shift>1/epsilon,then every k>=N has b_k<epsilon

Conditions: none

Increasing denominators and an Archimedean cutoff supply the all-later bound for every epsilon,not an inference from the displayed prefix.

Step identifiers and dependencies

Rule: harmonic_full_tail_terms_zero_not_observed_prefix · Uses: G001, S011

S013 · implies

Before

absolute series of declared alternating tail:same full absolute/positive series over denominators m=8,9,...

After

for every integer j>=0 large enough that2^j>=shift-1,the block m=2^j+1..2^(j+1) has2^j terms each>=1/2^(j+1);each block sum>=1/2;infinitely many disjoint blocks make partial sums unbounded

Conditions: none

Removing finitely many initial terms leaves the dyadic-block argument.Each sufficiently late block contributes at least1/2,so arbitrarily many disjoint blocks force unbounded partial sums.Terms tending to zero do not give a finite limit of partial sums.

Step identifiers and dependencies

Rule: harmonic_shifted_dyadic_blocks_diverge_not_term_limit · Uses: G001, S012

S014 · implies

Before

WHOLE declared terms=(-1)^k/(k+8),k starts0 positive;displayed first5 terms=[1/8, -1/9, 1/10, -1/11, 1/12]

After

b_k positive decreasing to0;even S_2m increases by b_2m-b_(2m+1)>=0;odd S_(2m+1) decreases;0<=S_2m<=S_(2m+1)<=b_0=1/8;gap b_2m tends0

Conditions: none

Positive decreasing magnitudes make even partial sums increase and odd partial sums decrease while bounding one another.Real completeness gives both limits,and their vanishing gap makes them equal,so the whole partial-sum sequence converges.Alternation or a term-zero condition alone is not a general criterion.

Step identifiers and dependencies

Rule: absseries_alternating_monotone_subsequences_not_alternation_alone · Uses: G001, S013

S015 · calculation

Before

alternating displayed exact partial sum := sum(1/8, -1/9, 1/10, -1/11, 1/12)

After

alternating displayed exact partial sum = 421/3960

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S014

S016 · calculation

Before

alternating next-term remainder denominator := sum(5, 8)

After

alternating next-term remainder denominator = 13

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S015

S017 · calculation

Before

alternating next-term absolute remainder bound := div(1, 13)

After

alternating next-term absolute remainder bound = 1/13

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S016

S018 · calculation

Before

alternating next signed term := mul(-1, 1/13)

After

alternating next signed term = -1/13

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S017

S019 · calculation

Before

alternating next exact partial sum := sum(421/3960, -1/13)

After

alternating next exact partial sum = 1513/51480

Conditions: none

Compute exactly from original roles and established intermediates,retaining denominators,signs,indices and strict conditions.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S018

S020 · implies

Before

displayed S_n=421/3960;adjacent S_(n+1)=1513/51480;n=5;positive shift=8

After

common limit L lies between these two endpoints;abs(L-S_n)<=1/13;original series converges=Yes;absolute harmonic series converges=No

Conditions: none

The whole-tail alternating certificate traps the common limit between adjacent partial sums and gives the next-term error bound.The separate dyadic argument proves divergence of the absolute series.Both certificates establish conditional convergence;the displayed finite list alone proves neither infinite claim.

Step identifiers and dependencies

Rule: absseries_conditional_requires_convergence_and_absolute_divergence · Uses: G001, S019

Reverse checks

  • S020 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S019 · premise_and_result_audit — Recompute alternating next exact partial sum with exact rational arithmetic, not rounded decimals.
  • S018 · premise_and_result_audit — Recompute alternating next signed term with exact rational arithmetic, not rounded decimals.
  • S017 · premise_and_result_audit — Recompute alternating next-term absolute remainder bound with exact rational arithmetic, not rounded decimals.
  • S016 · premise_and_result_audit — Recompute alternating next-term remainder denominator with exact rational arithmetic, not rounded decimals.
  • S015 · premise_and_result_audit — Recompute alternating displayed exact partial sum with exact rational arithmetic, not rounded decimals.
  • S014 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S013 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S012 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S011 · premise_and_result_audit — Recompute alternating displayed term4 signed value with exact rational arithmetic, not rounded decimals.
  • S010 · premise_and_result_audit — Recompute alternating displayed term4 denominator with exact rational arithmetic, not rounded decimals.
  • S009 · premise_and_result_audit — Recompute alternating displayed term3 signed value with exact rational arithmetic, not rounded decimals.
  • S008 · premise_and_result_audit — Recompute alternating displayed term3 denominator with exact rational arithmetic, not rounded decimals.
  • S007 · premise_and_result_audit — Recompute alternating displayed term2 signed value with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute alternating displayed term2 denominator with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Recompute alternating displayed term1 signed value with exact rational arithmetic, not rounded decimals.
  • S004 · premise_and_result_audit — Recompute alternating displayed term1 denominator with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute alternating displayed term0 signed value with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute alternating displayed term0 denominator with exact rational arithmetic, not rounded decimals.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(8, 5, [1/8, -1/9, 1/10, -1/11, 1/12], Yes, No, alternating_remainder_and_harmonic_absolute_divergence)

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.

Source hashes and review receipts
  • input commit: 0f7be61e2c22317a4075561dc822c87d881a50db
  • original question SHA-256: 671273651f65d6d4e1ffda302070670bd84775dc7eb9ea1e355b771600efb899
  • candidate record SHA-256: 9857fb2ca3a60bc5a35e8ecf560a2b9c502e9ce086d1e8309545253d87c14015
  • semantic review receipt SHA-256: f73d099ebe3ff1c69a5d96f08c75b11b9e5b05120af40cf3ef388fce3b5c5336
  • question-first witness SHA-256: 22675ffb6209b4fea076032b29b96e3dc19aad4244c54493f5f65f5e5d875699
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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