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Question 23826: A Whole Geometric Coefficient Law Gives an Exact Radius

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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R0046-23826 · q-20261014-advance-20261112-r05-power-series-radius-of-convergence-0001

Original question and givens

Use a_n=(1/2)^n for every n≥0, positive ratio q=1/2, and center c=-12. Give (coefficient_law, center, radius, interior_status, exterior_status, boundary).

  • G001 — Use a_n=(1/2)^n for every n≥0, positive ratio q=1/2, and center c=-12. Give (coefficient_law, center, radius, interior_status, exterior_status, boundary).

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=radius-geometric-exact;original snapshot and mathematics retained

After

explicit ordered source output fields=[coefficient_law, center, radius, interior_status, exterior_status, boundary]

Conditions: none

Keep the source snapshot while listing ordered fields without JavaScript.Radius uses its original mode to select6 or11 fields without padding;distinguish nonclaims from actual negations.

Step identifiers and dependencies

Rule: source_ordered_interface_explicit_without_javascript · Uses: G001

S002 · calculation

Before

Radius ORIGINAL positive coefficient-ratio reciprocal := div(1, 1/2)

After

Radius ORIGINAL positive coefficient-ratio reciprocal = 2

Conditions: none

Substitute original roles and established intermediates exactly,without floats or treating finite tests as universal limits.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · implies

Before

ORIGINAL WHOLE a_n=(1/2)^n for EVERY n>=0;center=-12;positive q=1/2

After

absolute geometric term ratio=q*|x-center|;less than1 gives absolute convergence,greater than1 makes terms not tend0;exact radius1/q=2

Conditions: none

Use the law for every n,not a handful of coefficients.Keep interior and exterior separate and audit endpoints separately;a radius does not replace endpoint conclusions.

Step identifiers and dependencies

Rule: radius_WHOLE_geometric_inside_outside_not_finite_coefficients · Uses: G001, S002

Reverse checks

  • S003 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S002 · premise_and_result_audit — Recompute Radius ORIGINAL positive coefficient-ratio reciprocal 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

(a_n=(1/2)^n_for_every_n>=0, -12, 2, absolute_convergence_inside, divergence_outside, endpoints_require_separate_audit)

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: c5c69f1480bffbcb45ae9af6912c6496fce92045eba9606293c259109318d161
  • candidate record SHA-256: a0916214f9bf0efc5218cc245cac1811afb670bda4363babea0034763142c94f
  • semantic review receipt SHA-256: a7c0d888ade6d307703c4222c4137c78c0d2448babdcba2fa3446fe6fdd343c1
  • question-first witness SHA-256: c9571f97a37d503ad6a61034cc00108543a05c37ef246d1c4962f55136a3de02
  • Lean: NOT_RUN · human review: NOT_PERFORMED
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