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

Toán Lớp 6: A= 1+3+3 ∧2+3 ∧3+-.+3 ∧ 2008

Toán Lớp 6: A= 1+3+3 ∧2+3 ∧3+…..+3 ∧ 2008

Comments ( 2 )

  1. Giải đáp:
    A=(3^2009-1)/2
    Lời giải và giải thích chi tiết:
     A=1+3+3^2+3^3+…+3^2008
    3A=3+3^2+3^3+3^4+…..+3^2009
    3A-A=(3+3^2+3^3+3^4+…..+3^2009)-(1+3+3^2+3^3+…+3^2008)
    2A=3+3^2+3^3+3^4+…+3^2009-1-3-3^2-3^3-….-3^2008
    2A=(3-3)+(3^3-3^2)+(3^3-3^3)+(3^4-3^4)+….+(3^2008-3^2008)+(3^2009-1)
    2A=3^2009-1
    A=(3^2009-1)/2
    Vậy A=(3^2009-1)/2

  2. A=1+3+3^2+3^3+…+3^2008
    =>3A=3+3^2+3^3+3^4+…+3^2009
    =>3A-A=(3+3^2+3^3+3^4+…+3^2009)-(1+3+3^2+3^3+…+3^2008)
    =>2A=3^2009-1
    =>A=(3^2009-1)/2

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