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

Toán Lớp 6: Tìm số tự nhiên x biết 3^x+2 + 3^x-1 = 252

Toán Lớp 6: Tìm số tự nhiên x biết 3^x+2 + 3^x-1 = 252

Comments ( 2 )

  1. 3^(x+2)+3^(x-1)=252
    3^x . 3^2 + 3^x : 3^1=252
    3^x . 9 + 3^x . 1/3 =252
    3^x . (9 + 1/3)=252
    3^x . 28/3=252
    3^x=252 :28/3
    3^x=27
    3^x=3^3
    ->x=3

  2. 3^(x+2)+3^(x-1)=252
    =>3^x .3^2+3^x .3^(-1)=252
    =>3^x .9+3^x . 1/3=252
    =>3^x .(9+1/3)=252
    =>3^x=27
    =>3^x=3^3
    =>x=3

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