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1/9,2/27,1/27,()

1/3,2/9,4/27,8/81,…… 是首项为1/3,公比为2/3的等比数列 用等比数列求和公式得:S=1/3+2/9+4/27+8/81+……+2的n-1次方/3的n次方 =1/3[1-(2/3)^n]/(1/2/3) =1-(2/3)^n =(3^n-2^n)/3^n 如果你没学过的话,可以设: S=1/3+2/9+4/27+8/81+……+2的n-1次...

1/27÷2/9 =1/27×9/2 =3/2

1/6*3=1/2 1/2*3=(3/2) 3/2*3=9/2 9/2*3=27/2 27/2*3=(81/2) 规律:前一项乘以3得出后一项 所以(3/2),(81/2)为所求

1/3,1/9,1/27,1/81……这列数的每一项越来越小,越来越接近(0),这列数的总和是(1-1/3^n)/2

选A 1/6÷1/2=1/3 1/9÷1/6=2/3 1/9÷1/9=3/3 4/27÷1/9=4/3 x÷4/27=5/3 即,x=20/81

1/27 = 3/81 1/9, 2/27, 3/81, 4/(3*81)=4/243 分子依次加1,分母乘3。 第四个数是4/243

1/9等于几分之二等于27分之几 1/9 =18分之2 =27分之3

分子是2的n-2次,分母是3的n-1次

(8/9+1/3-2/27)×2.7 = 8/9 ×2.7+1/3 ×2.7 - 2/27 ×2.7 =2.4+0.9 -0.2 =3.1

1-2/3-2/9-2/27-2/81-2/243-2/729 =1-2/3-2/9-2/27-2/81-2/243-2/729-1/729+1/729 =1-2/3-2/9-2/27-2/81-2/243-3/729+1/729 =1-2/3-2/9-2/27-2/81-2/243-1/243+1/729 =1-2/3-2/9-2/27-2/81-1/81+1/729 =1-2/3-2/9-2/27-1/27+1/729 =1-2/3-2/9-1/...

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