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7x - 7 - 5x - 35 = 0

2x + 28 = 0

2x = -28

x = -14 

Bài 2: 

a: =>x/4=1/8

hay x=1/2

b: \(\Leftrightarrow\dfrac{x}{-5}=\dfrac{11}{6}\)

hay x=-55/6

c: \(\Leftrightarrow\dfrac{-3.5}{x}=\dfrac{4.25}{8}\)

hay x=-112/17

\(\frac{x-3}{5-x}=\frac{5}{7}\)

\(\Leftrightarrow\left(x-3\right).7=5.\left(5-x\right)\)

\(\Leftrightarrow7x-21=25-5x\)

\(\Leftrightarrow7x+5x=25+21\)

\(\Leftrightarrow12x=46\)

\(\Leftrightarrow x=\frac{46}{12}=\frac{23}{6}\)

Vậy x = \(\frac{23}{6}\)

7x-21=25-5x

12x=46

x=23/6

Câu a:

0,4 : x = x : 0,9

x^2 = 0,4 x 0,9

x^2 = 0,36

x^2 = (0,6)^2

x = - 0,6 hoặc x = 0,6

Vậy x ∈ {-0,6; 0,6}

Câu b:

13\(\frac13\) : 1\(\frac13\) = 26 : (2x - 1)

\(\frac{40}{13}\) : \(\frac43\) = 26 :(2x - 1)

\(\frac{40}{13}\) x \(\frac34\) = 26 :(2x - 1)

\(\frac{30}{13}\) = 26 : (2x - 1)

26 : \(\frac{30}{13}\) = 2x - 1

26 x \(\frac{13}{30}\) = 2x - 1

169/15 = 2x - 1

2x = 169/15 + 1

2x = 184/15

x = 184/15 : 2

x = 184/15 x 1/2

x = 92/15

Vậy x = 92/15

\(\text{a)}\frac{37-x}{x+13}=\frac{3}{7}\)

\(\Leftrightarrow3\left(x+13\right)=7\left(37-x\right)\)

\(\Leftrightarrow3x+39=259-7x\)

\(\Leftrightarrow3x+7x=259-39\)

\(\Leftrightarrow10x=220\)

\(\Leftrightarrow x=22\)

\(\text{b)}\frac{x+4}{20}=\frac{5}{x+4}\)

\(\Leftrightarrow\left(x+4\right)^2=100\)

\(\Leftrightarrow\orbr{\begin{cases}x+4=10\\x+4=-10\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=6\\x=-14\end{cases}}\)

Bài 1a:

\(\frac{4,6}{1,4}\) = \(\frac{11,5}{5x}\)

4,6 x 5\(x\) = 11,5 x 1,4

23\(x\) = 16,1

\(x\) = 16,1 : 23

\(x\) = 0,7

Vậy \(x\) = 0,7

Bài 1b:

\(\frac{x^2}{6}\) = \(\frac{24}{25}\)

25\(x^2\) = 24.6

25\(x^2\) = 144

\(x^2\) = 144/25

\(x\) = - 12/5 hoặc \(x\) = 12/5

Vậy \(x\) ∈ {-12/5; 12/5}

Bài 1c:

\(\frac{x+2}{2}\) = \(\frac{1}{1-x}\)

(\(x\) + 2)(1 - \(x\)) = 1.2

\(x\) - \(x^2\) + 2 - 2\(x\) = 2

\(x^2\) + (2\(x\) - \(x\)) + 2 - 2 = 0

\(x^2\) + \(x\) + 0 = 0

\(x\)(\(x\) + 1) = 0

\(x\) = 0

\(x\) + 1 = 0

\(x\) = - 1

Vậy \(x\) ∈ {-1; 0}

a) \(\frac{3x-2}{1\frac{2}{5}}=\frac{2\frac{3}{7}}{2\frac{3}{5}}\Rightarrow3x-2=1.\frac{2}{5}.\frac{2\frac{3}{7}}{2\frac{3}{5}}=\frac{7}{5}.\frac{17}{7}.\frac{5}{13}\)

\(3x-2=\frac{17}{13}\Rightarrow3x=2+\frac{17}{13}=\frac{43}{13}\Rightarrow x=\frac{43}{39}.\)

b) \(\frac{x}{0,16}=\frac{9}{x}\Rightarrow x^2=9.0,16=1,44\Rightarrow x=\pm1,2\)

a) \(\frac{x}{7}=\frac{18}{14}\)

\(\frac{x}{7}=\frac{9}{7}\)

\(\Rightarrow x=9\)

b) \(6:x=1\frac{3}{4}:5\)

\(6:x=\frac{7}{4}.\frac{1}{5}\)

\(6:x=\frac{7}{20}\)

\(x=6:\frac{7}{20}\)

\(x=\frac{120}{7}\)

vay \(x=\frac{120}{7}\)

c) \(\frac{5,7}{0,35}=\frac{-x}{0,45}\)

\(\Rightarrow-0,35x=5,7.0,45\)

\(\Rightarrow-0,35x=2,565\)

\(\Rightarrow x=\frac{-2,565}{0,35}\)

\(\Rightarrow x=\frac{-513}{70}\)

vay \(x=\frac{-513}{70}\)