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

Toán Lớp 5: Tính nhanh: `A=1+1/3+1/9+1/27+1/81+1/243+1/729`

Tháng Một 9, 2023 Toán học 2 Comments 0 views

Toán Lớp 5: Tính nhanh:
A=1+1/3+1/9+1/27+1/81+1/243+1/729

Comments ( 2 )

  1. dongoclandiem
    dongoclandiem
    9 Tháng Một, 2023 at 9:38 sáng
    Reply
    A = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729
    3 xx A = 3 xx ( 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729 )
    3 xx A = 3 + 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243
    3 xx A – A = ( 3 + 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 ) – ( 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729 )
    2 xx A = 3 – 1/729
    2 xx A = 2186/729
    A = 2186/729 : 2
    A = 1093/729
    Vậy , A = 1093/729 .

  2. tuminh25
    tuminh25
    9 Tháng Một, 2023 at 9:38 sáng
    Reply
    A=1+1/3+1/9+1/27+1/81+1/243+1/729
    Axx3=(1+1/3+1/9+1/27+1/81+1/243+1/729)xx3
    Axx3=3+1+1/3+1/9+1/27+1/81+1/243+1/729-1/729
    Axx3=3+A-1/729
    Axx2=3-1/729
    Axx2=2186/729
    A=2186/729 :2
    A=1093/729
    Vậy A=1093/729

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

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