lean_workbook_plus_76467

Proved

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

Since $a+b+c=0$ , $-a-b=c$ . So: $a^{2}+b^{2}+c^{2}=a^{2}+b^{2}+(-a-b)^{2}=2a^{2}+2ab+2b^{2}$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_76467 : ∀ a b c : ℝ, a + b + c = 0 → a^2 + b^2 + c^2 = 2 * a^2 + 2 * a * b + 2 * b^2   :=  by sorry

Source