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

Toán Lớp 5: Bài 2: tính nhanh tổng sau: A= 1/3 + 1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192

Toán Lớp 5: Bài 2: tính nhanh tổng sau:
A= 1/3 + 1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192

Comments ( 2 )

  1. Giải đáp + Lời giải và giải thích chi tiết:
    $#pro2k9$
     Bài 2:
    A = 1/3 + 1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192
    1/2 A = 1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192 + 1/384
     A – 1/2A = (1/3 + 1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192)  – (1/6 + 1/12 + 1/24 + 1/48 + 1/96 + 1/192 + 1/384)
    1/2A = 1/3 – 1/384
    1/2A = 128/384 – 1/384
    1/2A = 127/384
    A      = 127/384 : 1/2
    A     = 127/192

  2. =2 x (1/3+1/6+1/12+1/24+1/48+1/96+1/192
    =2 x (1-1/3+1/3-1/6+1/6-1/12+1/12-1/24+1/24-1/48+1/48-1/96+1/96-1/192)
    =2 x (1-1/192)
    =2 x 191/192
    =382/192
    =191/96

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