Các b giúp mình với mình đanh cần gấp

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Các b giúp mình với mình đanh cần gấp
cac-b-giup-minh-voi-minh-danh-can-gap

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Bơ 6 years 2020-11-24T12:06:04+00:00 1 Answers 103 views 0

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  1. Philomena
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    2020-11-24T12:07:47+00:00
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    Bài 5:

    a) $3^n=81$

    $↔ 3^n=3^4$

    $↔ n=4$

    b) $4^n=64$

    $↔ 4^n=4^3$

    $↔ n=3$

    c) $25^n:5^3=5$

    $↔ (5^2)^n=5.5^3$

    $↔ 5^{2n}=5^4$

    $↔ 2n=4$

    $↔ n=2$

    d) $16^n:8^2=4^5$

    $↔ (2^4)^n:(2^3)^2=(2^2)^5$

    $↔ 2^{4n}:2^6=2^{10}$

    $↔ 2^{4n-6}=2^{10}$

    $↔ 4n-6=10$

    $↔ 4n=16$

    $↔ n=4$

    e) $2^5.3^5=6^n$

    $↔ (2.3)^5=6^n$

    $↔ 6^5=6^n$

    $↔ n=5$

    g) $36^n:18^n=4^2$

    $↔ (36:18)^n=(2^2)^2$

    $↔ 2^n=2^4$

    $↔ n=4$

    Bài 6:

    a) $8^3>2^n>4^3$

    $↔ (2^3)^3>2^n>(2^2)^3$

    $↔ 2^9>2^n>2^6$

    $↔ 6<n<9$

    $→ n∈\{7;8\}$

    b) $81>9^n>3$

    $↔ 3^4>(3^2)^n>3^1$

    $↔ 3^4>3^{2n}>3^1$

    $↔ 1<2n<4$

    $→ n=1$

    c) $125^2>5^n≥25$

    $↔ (5^3)^2>5^n≥5^2$

    $↔ 5^6>5^n≥5^2$

    $↔ 2≤n<6$

    $→ n∈\{2;3;4;5\}$

    d) $49^2>7^{n+1}>7$

    $↔ (7^2)^2>7^{n+1}>7^1$

    $↔ 7^4>7^{n+1}>7^1$

    $↔ 1<n+1<4$

    $↔ 0<n<3$

    $→ n∈\{1;2\}$

    e) $4^5≥2^n≥1024$

    $↔ (2^2)^5≥2^n≥2^{10}$

    $↔ 2^{10}≥2^n≥2^{10}$

    $↔ 2^n=2^{10}$

    $↔ n=10$

    g) $25^3>5^n>125$

    $↔ (5^2)^3>5^n>5^3$

    $↔ 5^6>5^n>5^3$

    $↔ 3<n<6$

    $→ n∈\{4;5\}$

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