lean_workbook_plus_31221

Proved

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

By average rate, we know that $\dfrac{2\times2x}{2+x}=3$ . Solving, we get $x=6$ , which is $B$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_31221  (x : ℝ)
  (h₀ : 0 < x)
  (h₁ : 2 * 2 * x / (2 + x) = 3) :
  x = 6   :=  by sorry

Source