Prove2Me

Lean-Workbook Plus 20381: Trigonometric identity

Proved
WorkbookRestored.plus_20381

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

lean-workbookrestored-importssource-checked

The special-angle tangent value is tan⁡(π/2+π/4)=−1\tan(\pi/2+\pi/4)=-1.

Source: Lean-Workbook row lean_workbook_plus_20381 (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_20381 (x : ℝ) : tan (π / 2 + π / 4) = -1   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_20381; immutable original Prove2Me node 7b74378e-1a91-493a-bd2a-96b4ada48ca6

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