Tìm x, biết a) x + 30%x = -1,3 b) ( 2x + 3/4 ) ( x 2 – 1/9 ) = 0 c) 7 ║ 3/5x – 40% ║ – 3/5 : 1/2 = 0,2 d) x-5/8 = 2/x-5

Question

Tìm x, biết
a) x + 30%x = -1,3
b) ( 2x + 3/4 ) (
x
2
– 1/9 ) = 0
c) 7 ║ 3/5x – 40% ║ – 3/5 : 1/2 = 0,2
d) x-5/8 = 2/x-5

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Melody 1 năm 2021-08-09T02:22:18+00:00 2 Answers 4 views 0

Answers ( )

    0
    2021-08-09T02:23:44+00:00

    Đáp án:

     a) x+30%x=-1,3

    ⇔1310x=-1,3

    ⇔x=-1

    Vậy x=-1

    b) (2x+34)(x2-19)=0

     [2x+34=0x2−19=0

     [x=−38x=29 

    Vậy S=−38;29

    c) 7|35x-40%|-35:12=0,2

    ⇔7|35x-40%|-65=0,2

    ⇔7|35x-40%|=75

    ⇔|35x-40%|=15

    [35x−25=1535x−25=−15

     [x=1x=13 

    Vậy S={1;13}

    d) x-58=2x-5

    ⇔(x-5)2=16

    ⇔x2-5x-5x+25=16

    ⇔x2-10x+9=0

    ⇔x2-x-9x+9=0

    ⇔x(x-1)-9(x-1)=0

    ⇔(x-9)(x-1)=0

     [x−9=0x−1=0

     [x=9x=1 

    Vậy 

     

    0
    2021-08-09T02:23:47+00:00

    Đáp án:

     

    Giải thích các bước giải:

     a) `x + 30%x = -1,3`

    `⇔ \frac{13}{10}x=-1,3`

    `⇔ x=-1`

    Vậy `x=-1`

    b) `(2x+3/4)(x/2-1/9)=0`

    `⇔` \(\left[ \begin{array}{l}2x+\dfrac{3}{4}=0\\\dfrac{x}{2}-\frac{1}{9}=0\end{array} \right.\)

    `⇔` \(\left[ \begin{array}{l}x=-\dfrac{3}{8}\\x=\dfrac{2}{9}\end{array} \right.\) 

    Vậy \(S={-\dfrac{3}{8};\dfrac{2}{9}}\)

    c) `7|3/5x-40%|-3/5:1/2=0,2`

    `⇔ 7|3/5x-40%|-6/5=0,2`

    `⇔ 7|3/5x-40%|=\frac{7}{5}`

    `⇔ |3/5x-40%|=\frac{1}{5}`

    `⇔`$\left[ \begin{array}{l} \dfrac{3}{5}x-\dfrac{2}{5}=\dfrac{1}{5} \\ \dfrac{3}{5}x-\dfrac{2}{5}=-\dfrac{1}{5}\end{array} \right.$

    `⇔` \(\left[ \begin{array}{l}x=1\\x=\dfrac{1}{3}\end{array} \right.\) 

    Vậy `S={1;1/3}`

    d) `\frac{x-5}{8}=\frac{2}{x-5}`

    `⇔ (x-5)^2=16`

    `⇔ x^2-5x-5x+25=16`

    `⇔ x^2-10x+9=0`

    `⇔ x^2-x-9x+9=0`

    `⇔ x(x-1)-9(x-1)=0`

    `⇔ (x-9)(x-1)=0`

    `⇔` \(\left[ \begin{array}{l}x-9=0\\x-1=0\end{array} \right.\)

    `⇔` \(\left[ \begin{array}{l}x=9\\x=1\end{array} \right.\) 

    Vậy `S={9;1}`

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