1+1.91+1.991+ …+1.9999991等于多少?

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1+1.91+1.991+…+1.9999991等于多少?1+1.91+1.991+…+1.9999991等于多少?1+1.91+1.991+…+1.9999991等于多少?1+1.91+1.991+

1+1.91+1.991+ …+1.9999991等于多少?
1+1.91+1.991+ …+1.9999991等于多少?

1+1.91+1.991+ …+1.9999991等于多少?
1+1.91+1.991+ …+1.9999991
=1+(2-0.09)+(2-0.009)+……+(2-0.0000009)
=(1+2×6)-(0.09+0.009+0.0009+……+0.0000009)
=13-0.0999999
=12.9000001
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原式=1+(2-0.01)+(2-0.001)+…………+(2-0.0000001)=13-0.0111111=12.9888889

12.9000001

  原式=1+2-0.09+2-0.009+……+2-0.0000009
  =1+2*6-(0.09+0.009+……+0.0000009)
  =13-0.0999999
  =12.9000001