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

Toán Lớp 6: A = 1+3^2 + 3^4 + 3^6 + – + 3^48

Toán Lớp 6: A = 1+3^2 + 3^4 + 3^6 + …. + 3^48

Comments ( 2 )

  1. Giải đáp:
    A=(3^50-1)/8 
    Lời giải và giải thích chi tiết:
    A=1+3^2+3^4+…+3^48
    to 3^2 A=9A=3^2+3^4+3^6+…+3^50
    to 9A-A=3^2+3^4+3^6+…+3^50-(1+3^2+3^4+…+3^48)
    to 8A=3^50-1
    to A=(3^50-1)/8

  2. A = 1+3^2 +3^4 +3^6 + … +3^48
    => 3^2A =3^2 +3^4 +3^6 +3^8 + … +3^48 +3^50
    => 3^2A – A = (3^2 +3^4 +3^6 +3^8 + … +3^48 +3^50) -( 1+3^2 +3^4 +3^6 + … +3^48)
    => 8A = 3^50 -1
    => A = (3^50-1)/8 
    Vậy A = (3^50-1)/8 . 
     

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