Tìm x: a) 3^x+1 = 9^7 b) 625/5^x = 5^3 c) (-2)^x/-128 = 4

Tìm x:
a) 3^x+1 = 9^7
b) 625/5^x = 5^3
c) (-2)^x/-128 = 4

0 thoughts on “Tìm x: a) 3^x+1 = 9^7 b) 625/5^x = 5^3 c) (-2)^x/-128 = 4”

  1. Đáp án:

     

    Giải thích các bước giải:

    $\text{a) $3^{x+1}$ = $9^{7}$.}$

    $\text{⇒ $3^{x+1}$ = $3^{14}$.}$

    $\text{⇒ x + 1 = 14.}$

    $\text{⇒ x = 14 – 1.}$

    $\text{⇒ x = 13.}$

    $\text{b) $\dfrac{625}{5^x}$ = $5^3$.}$

    $\text{⇒ $\dfrac{5^4}{5^x}$ = $5^3$.}$

    $\text{⇒ $5^{4-x}$ = $5^3$.}$

    $\text{⇒ 4 – x = 3.}$

    $\text{⇒ x = 4 – 3.}$

    $\text{⇒ x = 1.}$

    $\text{c) $\dfrac{(-2)^x}{-128}$ = 4.}$

    $\text{⇒ $\dfrac{(-2)^x}{(-2)^7}$ = $2^2$.}$

    $\text{⇒ $(-2)^{x-7}$ = $(-2)^2$.}$

    $\text{⇒ x – 7 = 2.}$

    $\text{⇒ x = 2 + 7.}$

    $\text{⇒ x =9.}$

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  2. a) `3^(x+1)` = `9^7`

    => `3^(x+1)` = `3^14`

    => x + 1 = 14

    => x = 13

    b) `625/5^x` = `5^3`

    => `5^4/5^x` = `5^3`

    => `5^x` = `5^1`

    => x = 1

    c) `(-2)^x/-128` = 4

    => `(-2)^x/(-2)^7` = `2^2`

    => `(-2)^x/(-2)^7` = `(-2)^2`

    => `(-2)^x` = `(-2)^2` . `(-2)^7`

    => `(-2)^x` = `(-2)^9`

    => x = 9

    XIN HAY NHẤT Ạ

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