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A normalized cubic sum with a pairwise quadratic correction

Proved
WorkbookSource.base_6962

by wamlart · Sep 13, 2026 · Mathlib 0df444a (Lean v4.33.1)

lean-workbooksource-checked

Let a,b,c>0 Prove that: a3+b3+c3abc+9ab+bc+aca2+b2+c2≥12 \frac {{a^3 + b^3 + c^3 }}{{abc}} + 9\frac {{ab + bc + ac}}{{a^2 + b^2 + c^2 }} \geq 12abca3+b3+c3​+9a2+b2+c2ab+bc+ac​≥12 I know it's easy but It is nice. It's must be like this: a3+b3+c3abc+9ab+bc+aca2+b2+c2≥12 \frac {{a^3 + b^3 + c^3 }}{{abc}} + 9\frac {{ab + bc + ac}}{{a^2 + b^2 + c^2 }} \geq 12abca3+b3+c3​+9a2+b2+c2ab+bc+ac​≥12 LHS−RHS=(∑a2−∑ab)(∑1ab−9∑ab)≥0 LHS - RHS = (\sum a^2 - \sum ab)(\sum \frac {1}{ab} - \frac {9}{\sum ab})\geq 0LHS−RHS=(∑a2−∑ab)(∑ab1​−∑ab9​)≥0

Source: InternLM Lean-Workbook, record lean_workbook_6962 (Apache-2.0). Complete source proposition preserved; proof developed independently.

Preamble
import Mathlib
open Real Nat
Formal statement
theorem WorkbookSource.base_6962 (a b c : ℝ) (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : (a^3 + b^3 + c^3) / (a * b * c) + 9 * (a * b + b * c + c * a) / (a^2 + b^2 + c^2) ≥ 12  :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_6962; Apache-2.0

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