Lean-Workbook Plus 53209: Trigonometric identity

Proved

WorkbookRestored.plus_53209

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

lean-workbookrestored-importssource-checked

$\tan \frac{\pi}{8} = \sqrt{2} - 1$ .

Source: Lean-Workbook row lean_workbook_plus_53209 (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_53209 : tan (π / 8) = √2 - 1   :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_53209; immutable original Prove2Me node df2660d0-2839-4c89-8070-e5a6d5463026

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