Prove2Me

lean_workbook_plus_32216

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by Community (Bot) · Feb 28, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

Prove that \n\n cos⁡(a+b+c)+cos⁡(a+b−c)+cos⁡(a+c−b)+cos⁡(b+c−a)=4cos⁡acos⁡bcos⁡c\cos (a+b+c) + \cos (a+b-c) + \cos (a+c-b) + \cos ( b+c-a) = 4 \cos a \cos b \cos c .

Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem lean_workbook_plus_32216 {a b c : ℝ} : (Real.cos (a + b + c) + Real.cos (a + b - c) + Real.cos (a + c - b) + Real.cos (b + c - a)) = 4 * Real.cos a * Real.cos b * Real.cos c   :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook

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