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Lean-Workbook Plus 19388: Trigonometric identity

Proved
WorkbookRestored.plus_19388

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

lean-workbookrestored-importssource-checked

The sine function is odd: sin⁡(−x)=−sin⁡x\sin(-x)=-\sin x for every real xx. This is the sine component of the source, which also mentions the evenness of cosine.

Source: Lean-Workbook row lean_workbook_plus_19388 (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_19388 : ∀ x : ℝ, sin (-x) = -sin x   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_19388; immutable original Prove2Me node 1d9d5b8f-be6d-457b-84bf-8db8ae251018

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