lean_workbook_plus_21180

Proved

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

When $x, y \in \mathbb{R}$ , then $f(2xy) = f(x) + f(y)$ . In addition, $f(2) = 7$ . Find $f(1)$ .

Preamble

import Mathlib.Analysis.Complex.Basic

Formal statement

theorem lean_workbook_plus_21180 (f : ℝ → ℝ) (hf : ∀ x y, f (2 * x * y) = f x + f y) : f 2 = 7 → f 1 = 7   :=  by sorry

Source