lean_workbook_plus_74356

Proved

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

Find the value of $x$ such that $f(g(f(g(x))))=20$ given $f(x)=4x-2$ and $g(x)=5x+3$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_74356 (x : ℝ) (f g : ℝ → ℝ) (hf : f = fun x => 4*x-2) (hg : g = fun x => 5*x+3) : f (g (f (g x))) = 20 ↔ x = -19/40   :=  by sorry

Source

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

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