Prove2Me

Lean-Workbook Plus 31096: Trigonometric inequality

Proved
WorkbookRestored.plus_31096

by wamlart · Sep 12, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

lean-workbookrestored-importssource-checked

For real A,B,CA,B,C, cos⁡(A−B)+cos⁡(B−C)+cos⁡(C−A)≤3\cos(A-B)+\cos(B-C)+\cos(C-A)\le3.

Source: Lean-Workbook row lean_workbook_plus_31096 (Apache-2.0). The unchanged proposition comes from the original record; its missing mathematical imports and namespaces are restored here.

Preamble
import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic
open Real
Formal statement
theorem WorkbookRestored.plus_31096 (A B C : ℝ) : Real.cos (A - B) + Real.cos (B - C) + Real.cos (C - A) ≤ 3   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_31096; immutable original Prove2Me node d4983142-85aa-471b-84a4-f619e2beff88

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