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

Toán Lớp 6: A = 1 + 2^1 + 2^1 + 2^2 + 2^3 + … + 2^2021 Tìm x thuộc N : 2^x = A + 1

Toán Lớp 6: A = 1 + 2^1 + 2^1 + 2^2 + 2^3 + … + 2^2021
Tìm x thuộc N : 2^x = A + 1

Comments ( 2 )

  1. A = 1 + 2^1 + 2^2 + 2^3 + … + 2^2021
    => 2A = 2^1 + 2^2 + 2^3 + 2^4 + … + 2^2022
    => 2A – A = ( 2^1 + 2^2 + 2^3 + 2^4 + … + 2^2022 ) – ( 1 + 2^1 + 2^2 + 2^3 + … + 2^2021 )
    => A = 2^2022 – 1
    Ta có :
    2^x = 2^2022 – 1 + 1
    => 2^x = 2^2022
    => x = 2022
    Vậy x = 2022
    #dtkc

  2. A = 1 + 2 + 2² + 2³ + ….. + $2^{2021}$ 
    → 2A = 2 + 2² + $2^{4}$ + …. + $2^{2022}$ 
    → A = 2A – A = (2 + 2² + $2^{4}$ + …. + $2^{2022}$) – (1 + 2 + 2² + 2³ + ….. + $2^{2021}$ )
                           = $2^{2022}$ – 1 
    $2^{x}$ = A + 1
    hay $2^{x}$ = $2^{2022}$ – 1 + 1
    ↔    $2^{x}$ = $2^{2022}$ 
    ↔    x = 2022 ™
     

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