题干
设a1，a2，a3为正数，求证：
+
+
≥a1+a2+a3 .
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| a |
| 3 |
| a |
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| a |
| 3 |
| a |
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| a |
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| a |
| 1 |
| a |
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答案(点此获取答案解析）
证明：不妨设a1≥a2≥a3＞0，于是
