lean_workbook_plus_40913

Proved

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

If $|ax^{2}+bx+c|\leq 1$ for all $x \in [-1,1]$ . Then

|a|+|b|+|c|\le 3

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_40913 (a b c : ℝ) (h : ∀ x ∈ Set.Icc (-1) 1, abs (a * x ^ 2 + b * x + c) ≤ 1) : abs a + abs b + abs c ≤ 3   :=  by sorry

Source