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January 如何证明 a－b ≤ a－c ＋ c－b
如何证明 a－b ≤ a－c ＋ c－b
∵X+Y≤X+Y
∴a-b=(a-c)+(c-b)≤a-c+c-b
设X=a-c,Y=c-b
原式变为│a-c+c-b│≤│a-c│＋│c-b│
有│X+Y│≤│X│+│Y│
∵│X+Y│≤│X│+│Y│
∴ a－b ≤ a－c ＋ c－b
最佳答案 - 由提问者2008-10-26 20:19:48选出
知识根据：x+y≤x+y
证明：
a-b
=(a-c)+(c-b)
≤a-c+c-b
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