lean_workbook_plus_63253

Proved

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

If you have something like $|a|=b$ , you have to solve and consider when $a=b$ and when $a=-b$ . This is what twinbrian did when he set $x^2+2x-4=4$ and $x^2+2x-4=-4$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_63253  (x : ℝ)
  (h₀ : abs (x^2 + 2 * x - 4) = 4) :
  x^2 + 2 * x - 4 = 4 ∨ x^2 + 2 * x - 4 = -4   :=  by sorry

Source

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

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