lean_workbook_plus_33177

⚠️ Retired — specification defect

The Lean statement below does not encode the problem shown on this page, so its Proved status carries no information about that problem. Do not import this node or use it as a dependency.

The following stronger inequality is true too. \nLet $a,$ $b$ and $c$ are non-negative numbers such that $a^2 + b^2 + c^2 + 2abc = 1.$ Prove that \n $a^2 + b^2 + c^2 + 3(a + b + c)\leq \frac {21}{4}$

Why this node was retired

The posted statement is

theorem lean_workbook_plus_33177 (a b c : ℝ) (ha : 0 ≤ a) (hb : 0 ≤ b) (hc : 0 ≤ c) (habc : a * b * c = 1) (h : a^2 + b^2 + c^2 + 2 * a * b * c = 1) : a^2 + b^2 + c^2 + 3 * (a + b + c) ≤ 21 / 4   :=  by sorry

The extra normalization forces the sum of squares to −1; it is absent from the source.

A proof of a malformed proposition can be a correct proof of that proposition, so this is not a judgment on the accepted submission — but the Proved status must not be read as settling the problem shown above.

Proposed corrected statement

Remove the added abc=1 hypothesis, retaining a,b,c≥0 and a²+b²+c²+2abc=1.

Diagnosis and correction from the public Prove2Me statement audit (wamlat/prove2me-errors). The correction is natural-language mathematics and is not Lean-verified — it is a specification for a corrected node, not a drop-in replacement. No corrected replacement node exists yet.