己知1⼀2+1⼀3等于5⼀6,1⼀3+1⼀4等于7⼀12,1⼀4+1⼀5等于9⼀20......试用简便方法计算3⼀2-5⼀6+

2024-11-17 12:28:49
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回答(1):

3/2-5/6+7/12-9/20+11/30-13/42+15/56
=1+1/2-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)
=1+1/2-1/2-1/3+1/3+1/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8
=1+1/8
=1又1/8(即9/8)