lean_workbook_plus_48471

Proved

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

Let be $x\in [-1,1]$ , and $a,b,c\in \mathbb{R}$ such that $|ax^2+bx+c|\le 1\ ,\ (\forall)x\in [-1,1]$ . Without second degree function prove that $|a|+|b|+|c|\le 4$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_48471 (a b c : ℝ) (h : ∀ x ∈ Set.Icc (-1) 1, abs (a * x ^ 2 + b * x + c) ≤ 1) :
  abs a + abs b + abs c ≤ 4   :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook

View graph