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

Toán Lớp 6: tìm x ( x thuộc N) 5^x = 125 3^2x = 81 5^2x-3 – 2.5 = 5^2.3

Toán Lớp 6: tìm x ( x thuộc N)
5^x = 125
3^2x = 81
5^2x-3 – 2.5 = 5^2.3

Comments ( 2 )

  1. 5^x=125
    5^x=5^3
    => x=3
    3^2x=81
    3^2x=3^4
    => 2x=4
    x=4 : 2
    x=2
    5^2x-3 – 2.5^2 = 5^2.3
    5^2x-3-2.25=25.3
    5^2x-3=25.3 + 2.25
    5^2x-3=25 . (2+3)
    5^2x-3=25.5
    5^2x-3=125
    5^2x-3=5^3
    =>2x-3=3
    2x=3+3
    2x=6
    x=6:2
    x=3

  2. 5^x = 125
    5^x = 5^3
    => x = 3
    Vậy x = 3
    3^(2x) = 81
    3^(2x) = 3^4
    => 2x = 4
    => x = 2
    Vậy x = 2
    5^(2x) – 3 – 2 . 5 = 5^2 . 3
    5^(2x) – 3 – 10 = 25 . 3
    5^(2x) – 3 – 10 = 75
    5^(2x) – 3 = 75 + 10
    5^(2x) – 3 = 85
    5^(2x) = 85 + 3
    5^(2x) = 88
    => Đề sai
    #dtkc

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

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