Prove2Me

Lean-Workbook Plus 38285: Trigonometric identity

Proved
WorkbookRestored.plus_38285

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

lean-workbookrestored-importssource-checked

If sin⁡x+cos⁡x=0.8\sin x+\cos x=0.8, then sin⁡3x+cos⁡3x=0.944\sin^3x+\cos^3x=0.944.

Source: Lean-Workbook row lean_workbook_plus_38285 (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_38285 (x : ℝ) (hx : sin x + cos x = 0.8) : sin x ^ 3 + cos x ^ 3 = 0.944   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_38285; immutable original Prove2Me node 54b1e59b-b629-418b-bb8a-338b582c74a1

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