高考问答老湿网 土豆:一道数学题目
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1/20+1/30+1/42+1/56+1/72+1/90=( )
需要详细解法
需要详细解法
1/20+1/30+1/42+1/56+1/72+1/90
=1/4*5+1/5*6+1/6*7+1/7*8+1/8*9+1/9*10
=1/4-1/5+1/5-1/6+***+1/9-1/10
=1/4-1/10
=3/20
1/20+1/30+1/42+1/56+1/72+1/90
=1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
=1/4-1/5+1/5-1/6+……+1/9-1/10
=1/4-1/10
=3/20
0.149 .
正确.
1/20+1/30+1/42+1/56+1/72+1/90
=1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
=(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1/4-1/10
=3/20
1/20+1/30+1/42+1/56+1/72+1/90
=1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
=(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10
=1/4-1/10
=3/20
1/20+1/30+1/42+1/56+1/72+1/90 = 0.149
0.05+0.033+0.024+0.017+0.014+0.011=0.149