Prove2Me

Lean-Workbook Plus 38361: Trigonometric inequality

Proved
WorkbookRestored.plus_38361

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

lean-workbookrestored-importssource-checked

For real a,ba,b, ∣cos⁡a∣+∣cos⁡b∣≥∣sin⁡(a+b)∣|\cos a|+|\cos b|\ge|\sin(a+b)|.

Source: Lean-Workbook row lean_workbook_plus_38361 (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_38361 (a b : ℝ) : |Real.cos a| + |Real.cos b| ≥ |Real.sin (a + b)|   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_38361; immutable original Prove2Me node ecfe76a0-b8fe-41ac-9907-95f1c84f76b8

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