A cyclic quadratic-product ratio lower bound

Proved

WorkbookSource.base_5776

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

lean-workbooksource-checked

Let $a, b, c>0$ . Prove that $\frac{ab}{c^2+ab+bc}+\frac{bc}{a^2+bc+ca}+\frac{ca}{b^2+ca+ab}\ge\frac{3}{4}$

Source: InternLM Lean-Workbook, record lean_workbook_5776 (Apache-2.0). Complete source proposition preserved; proof developed independently.

Preamble

import Mathlib
open Real Nat

Formal statement

theorem WorkbookSource.base_5776 (a b c : ℝ) (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : (a * b / (c * c + a * b + b * c) + b * c / (a * a + b * c + c * a) + c * a / (b * b + c * a + a * b)) ≥ 3 / 4  :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_5776; Apache-2.0

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