lean_workbook_plus_6172

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

Sum to product gives $\sin(20)+\sin(40)=2\sin(30)\cos(10)$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_6172 : ∀ a b c d : ℝ, a = 20 ∧ b = 40 → c = 30 ∧ d = 10 → sin a + sin b = 2 * sin c * cos d   :=  by sorry

Source