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

Toán Lớp 6: tính tổng sau A=1/2+1/2^2+-+1/2^2005

Toán Lớp 6: tính tổng sau A=1/2+1/2^2+….+1/2^2005

Comments ( 2 )

  1. Lời giải và giải thích chi tiết:
    A = 1/2 + 1/(2^2) + …………. + 1/(2^2005)
    2A = 1 + 1/2 + …………….. + 1/(2^2004)
    2A – A = (1 + 1/2 + …………….. + 1/(2^2004)) – (1/2 + 1/(2^2) + …………. + 1/(2^2005))
    A = 1 – 1/(2^2005)

  2. A = 1/2 + 1/2^{2} + … + 1/2^{2005}
    2A = 1 + 1/2 + … + 1/2004
    2A – A = 1 + 1/2 + … + 1/2004 – 1/2 – 1/2^{2} – … – 1/2^{2005}
    A = 1 – 1/2^{2005}
     

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