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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 7: tính ` 2/1.2-2/2.3=–.-2/8.9`

Toán Lớp 7: tính 2/1.2-2/2.3-……………..-2/8.9

Comments ( 2 )

  1. Đặt A=\frac{2}{1.2}-\frac{2}{2.3}-….-\frac{2}{8.9}
    A=2.(\frac{1}{1.2}-\frac{1}{2.3}-….-\frac{1}{8.9})
    A=2.(1-1/2+1/2-1/3+….1/8-1/9)
    A=2.(1-1/9)
    A=2. 8/9
    A=16/9

  2. 2/1.2-2/2.3-…-2/8.9
    =2.(1/1.2-1/2.3-…-1/8.9)
    =2.(1-1/2+1/2-1/3+1/3-…-1/8+1/8-1/9)
    =2.(1-1/9)
    =2. 8/9
    =16/9
     

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222-9+11+12:2*14+14 = ? ( )

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