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

1. 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

2. 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}