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问题: 1/2 - 1/6 -1/12 - 1/20 - 1/30 - 1/42 +41/42 =?

1/2 - 1/6 -1/12 - 1/20 - 1/30 - 1/42 +41/42 =?
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解答:

原试 = (1-1/2)-(1/2-1/3)-(1/3-1/4)-(1/4-1/5)-(1/5-1/6)-(1/6-1/7)+41/42 = 1-1+1/2 -1/2 .....+1/6-1/6+1/7+41/42 =47/42