lean_workbook_plus_46203

Proved

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

=\tfrac{\sqrt5}{4}(1+\tfrac14+\tfrac1{16}+...)=\tfrac{\sqrt5}{4}\cdot\tfrac43=\tfrac{\sqrt5}{3}$

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_46203 :
  ∑' k : ℕ, (1 / 4)^k * (Real.sqrt 5 / 4) = (Real.sqrt 5 / 3)   :=  by sorry

Source