Tìm số tự nhiên x . biết a, x mũ 3 = 27 5 mũ x = 625 b, 2 mũ x . 16 = 128 3 mũ x : 9 = 27 c, ( 2x + 1 ) mũ 3 = 27 ( x – 2 ) mũ 2 = ( x – 2 ) mũ 4

Question

Tìm số tự nhiên x . biết
a, x mũ 3 = 27
5 mũ x = 625
b, 2 mũ x . 16 = 128
3 mũ x : 9 = 27
c, ( 2x + 1 ) mũ 3 = 27
( x – 2 ) mũ 2 = ( x – 2 ) mũ 4

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Nem 4 years 2020-11-11T14:02:49+00:00 2 Answers 204 views 0

Answers ( )

  1. minhkhoi
    0
    2020-11-11T14:04:04+00:00
    Reply

    Giải thích các bước giải:

    a) * `x^3 = 27`

    `=> x^3 = 3^3`

    `=> x = 3`

    * `5^x = 625`

    `=> 5^x = 5^4`

    `=> x = 4`

    b) * `2^x . 16 = 128`

    `=> 2^x . 2^4 = 2^7`

    `=> 2^x = 2^7 : 2^4`

    `=> 2^x = 2^3`

    `=> x = 3`

    * `3^x : 9 = 27`

    `=> 3^x : 3^2 = 3^3`

    `=> 3^x = 3^3 . 3^2`

    `=> 3^x = 3^5`

    `=> x = 5`

    c) * `(2x + 1)^3 = 27`

    `=> (2x + 1)^3 = 3^3`

    `=> 2x + 1 = 3`

    `=> 2x = 2`

    `=> x = 1`

    * Bn xem hình

    Study well !

    tim-so-tu-nhien-biet-a-mu-3-27-5-mu-625-b-2-mu-16-128-3-mu-9-27-c-2-1-mu-3-27-2-mu-2-2-mu-4

  2. Nick
    0
    2020-11-11T14:04:28+00:00
    Reply

    Bơơ

    a, $x^3=27$
    $⇒x^3=3^3$
    $⇒x=3$

    $5^x=625$
    $⇒5^x=5^4$
    $⇒x=4$

    b, $2^x.16=128$
    $2^x=128:16$
    $2^x=8$
    $⇒2^x=2^3$

    $⇒x=3$
    $3^x:9=27$
    $3^x=27.9$
    $3^x=243$
    $⇒3^x=3^5$
    $⇒x=5$

    c, $(2x+1)^3=27$
    $⇒(2x+1)^3=3^3$
    $⇒2x+1=3$
    $2x=3-1$

    $2x=2$
    $x=2:2$
    $x=1$

    $(x-2)^2=(x-2)^4$
    $(x-2)^2-(x-2)^4=0$
    $(x-2)^2.1-(x-2)^2.(x-2)^2=0$
    $(x-2)^2.(1-x+2)=0$

    $TH1: (x-2)^2=0$
    $x-2=0$
    $x=0+2$
    $x=2$

    $TH2: 1-x+2=0$
    $1-x=0-2$
    $1-x=-2$
    $x=1–2$
    $x=3$
    Vậy `x∈{2,3}`

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