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

Toán Lớp 6: Tìm số tự nhiên x , biết $5^{x}$ + $5^{x + 1}$ + $5^{x + 2}$ = 3875

Toán Lớp 6: Tìm số tự nhiên x , biết
$5^{x}$ + $5^{x + 1}$ + $5^{x + 2}$ = 3875

Comments ( 2 )

  1. 5^x + 5^{x + 1} + 5^{x +2} = 3875
    5^x + 5^x . 5 + 5^x + 25 = 3875
    5^x . (1 + 5 + 25) = 3875
    5^x . 31 = 3875
    5^x = 3875 : 31
    5^x = 125
    5^x = 5^3
    x = 3
    Vậy x = 3
     

  2. 5^x + 5^( x + 1) + 5^( x + 2) = 3875
    5^x + 5^x . 5 + 5^x . 25 = 3875
    5^x . ( 1 + 5 + 25) = 3875
    5^x . 31 = 3875
    5^x = 3875 : 31
    5^x= 125
    5^x = 5^3
    => x = 3
    Vậy x = 3
    #câty09
     

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