lean_workbook_plus_4590

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

Express $\sqrt{2}$ in terms of cosine: $\sqrt{2} = 2\cos\left(\frac{\pi}{4}\right)$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_4590 : 2 * Real.cos (Real.pi / 4) = Real.sqrt 2   :=  by sorry

Source