Prove2Me

Lean-Workbook Plus 9318: Trigonometric identity

Proved
WorkbookRestored.plus_9318

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

lean-workbookrestored-importssource-checked

The special-angle values satisfy cos⁡(π/2)+cos⁡(3π/2)=0+0\cos(\pi/2)+\cos(3\pi/2)=0+0.

Source: Lean-Workbook row lean_workbook_plus_9318 (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_9318 : Real.cos (π / 2) + Real.cos (3 * π / 2) = 0 + 0   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_9318; immutable original Prove2Me node 6978a4f3-2df4-46e4-8805-6eb1cef9897b

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