原式=2-(1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9)*8
=2-(1/4-1/9)*8
=2-8/4+8/9
=8/9
2-(1/20+1/30+1/42+1/56+1/72)*8这道题如何简便计算?
1个回答
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