Lean-Workbook Plus 35079: Trigonometric identity

Proved

WorkbookRestored.plus_35079

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

lean-workbookrestored-importssource-checked

$\cos(\pi/7)-\cos(5\pi/7)=\cos(\pi/7)-\cos(3\pi/7)+\cos(2\pi/7)-\cos(4\pi/7)$ .

Source: Lean-Workbook row lean_workbook_plus_35079 (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_35079 : cos (π / 7) - cos (5 * π / 7) = cos (π / 7) - cos (3 * π / 7) + cos (2 * π / 7) - cos (4 * π / 7)   :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_35079; immutable original Prove2Me node de557b64-aa6b-4dc3-a5f1-7c18dbc2a621

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