Two symmetric polynomial evaluations

Proved

WorkbookSource.problem_3217

by wamlart · Sep 12, 2026 · Mathlib 0df444a (Lean v4.33.1)

lean-workbooksource-checked

What is $f(-2021)+f(2019)$ ? $f(x)=x^5+5x^4+10x^3+10x^2-2x+1$

Source: InternLM Lean-Workbook, record lean_workbook_3217 (Apache-2.0). The complete source proposition and its explicit variable declarations are preserved.

Preamble

import Mathlib
open Real Nat

Formal statement

theorem WorkbookSource.problem_3217 (f : ℤ → ℤ) (f_def : ∀ x, f x = x^5 + 5 * x^4 + 10 * x^3 + 10 * x^2 - 2 * x + 1) : f (-2021) + f (2019) = 14  :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_3217; Apache-2.0

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