PUMaC 2007 · 个人决赛（A 组） · 第 1 题
PUMaC 2007 — Individual Finals (Division A) — Problem 1
题目详情
- Suppose that A is a set of integers. Denote the number of elements in A by | A | . Define A + A = { a + a : a , a ∈ A } and A − A = { a − a : a , a ∈ A } . Prove or disprove: for any set A, we 1 2 1 2 1 2 1 2 have the inequality | A − A | ≥ | A + A | .
解析
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Original Explanation
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