首先看：首先看：9/20 =1/4 +1/5
11/30 =1/5 +1/6
13/42 =1/6 +1/7
15/56 =1/7 +1/8
原式=1+1/4-（1/4+1/5）+1/5+1/6-（1/6+1/7）+1/7+1/8
=1+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
我打出来的分数在这里不认可，只能这样了，不知道你是否看得明白。
1又1/4-9/20+11/30-13/42+15/56=(1+1/4)-[(4+5)/(4×5)]+[(5+6)/(5×6)]-[(6+7)/(6×7)+[(7+8)/(7×8)]=(1+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1/7+1/8)=1+(1/8)=9/8(或化为带分数:"1又1/8")。
1又1/4-9/20+11/30-13/42+15/56 =5/4-9/20+11/30-13/42+15/56 =5/4-（1/4+1/5）+（1/5+1/6）-（1/6+1/7）+（1/7+1/8） =5/4-1/4-1/5+1/5+1/6-1/6-1/7+1/7+1/8 =（5/4-1/4）+（1/5-1/5）+（1/6-1/6）+（1/7-1/7)+1/8 =1+1/8 =9/8
太麻烦了!!!!!!!!!!!!
答：5/4-9/20+11/30-13/42+15/56-17/72+19/90 =(1+1/4)-(1/4+1/5)+(1/5+1/6)-(1/6+1/7)+(1...详情>>
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