lean_workbook_plus_11048

Proved

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

We have to prove the inequality $a^2+b^2+c^2+d^2\geq ac+bd+cb+da$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_11048 (a b c d : ℝ) : a ^ 2 + b ^ 2 + c ^ 2 + d ^ 2 ≥ a * c + b * d + c * b + d * a   :=  by sorry

Source