lean_workbook_plus_52651
ProvedArithmetic Mean - Quadratic Mean (or Root-Mean Square, you might know it as that) exactly as used above.
Preamble
import Mathlib.Analysis.Complex.Basic
Formal statement
theorem lean_workbook_plus_52651 (a b c : ℝ) : (a + b + c) / 3 ≤ Real.sqrt ((a ^ 2 + b ^ 2 + c ^ 2) / 3) := by sorry
Source