\(-\dfrac{4}{7}-x=\dfrac{3}{5}-2x\\ \Rightarrow-x+2x=\dfrac{3}{5}+\dfrac{4}{7}\\ \Rightarrow x=\dfrac{21}{35}+\dfrac{20}{35}\\ \Rightarrow x=\dfrac{41}{35}\)

Vậy `x=41/35`

__

\(\dfrac{3}{7}x-\dfrac{2}{3}x=\dfrac{10}{21}\\ \Rightarrow\left(\dfrac{3}{7}-\dfrac{2}{3}\right)x=\dfrac{10}{21}\\ \Rightarrow\left(\dfrac{9}{21}-\dfrac{14}{21}\right)x=\dfrac{10}{21}\\ \Rightarrow\dfrac{-5}{21}x=\dfrac{10}{21}\\ \Rightarrow x=\dfrac{10}{21}:\left(-\dfrac{5}{21}\right)\\ \Rightarrow x=-2\)

Vậy `x=-2`

a)

-4/7 - x = 3/5 - 2x

2x - x = 3/5 + 4/7

x = 41/35

Vậy x = 41/35

b)

3/7.x - 2/3.x = 10/21

x(3/7 - 2/3) = 10/21

x.(-5/21) = 10/21

x = 10/21 : (-5/21) = -2

Vậy x = -2

\(x\div4\frac{1}{3}=-2,5\)

\(\Leftrightarrow x\div\frac{13}{3}=\frac{-5}{2}\)

\(\Leftrightarrow x=\frac{-5}{2}.\frac{13}{3}\)

\(\Leftrightarrow x=\frac{-65}{6}\)

\(x\div\frac{-3}{5}=\frac{-10}{21}\)

\(\Leftrightarrow x=\frac{-10}{21}.\frac{-3}{5}\)

\(\Leftrightarrow x=\frac{30}{105}\)

\(\Leftrightarrow x=\frac{2}{7}\)

\(\frac{2}{3}x-\frac{1}{2}=\frac{1}{10}\)

\(\Leftrightarrow\frac{2}{3}x=\frac{1}{10}+\frac{1}{2}\)

\(\Leftrightarrow\frac{2}{3}x=\frac{6}{10}\)

\(\Leftrightarrow x=\frac{6}{10}\div\frac{2}{3}\)

\(\Leftrightarrow x=\frac{18}{20}\)

\(\Leftrightarrow x=\frac{9}{10}\)

\(\frac{1}{2}x+\frac{1}{2}=\frac{5}{2}\)

\(\Leftrightarrow\frac{1}{2}\left(x+1\right)=\frac{5}{2}\)

\(\Leftrightarrow\left(x+1\right)=\frac{5}{2}\div\frac{1}{2}\)

\(\Leftrightarrow\left(x+1\right)=5\)

\(\Leftrightarrow x=5-1\)

\(\Leftrightarrow x=4\)

\(\frac{-2}{3}-\frac{1}{3}\left(2x-5\right)=\frac{3}{2}\)

\(\Leftrightarrow\frac{-2}{3}-\frac{2x}{3}+\frac{5}{3}=\frac{3}{2}\)

\(\Leftrightarrow1-\frac{2x}{3}=\frac{3}{2}\)

\(\Leftrightarrow\frac{2x}{3}=1-\frac{3}{2}\)

\(\Leftrightarrow\frac{2x}{3}=\frac{-1}{2}\)

\(\Leftrightarrow x=\frac{-1}{2}\div\frac{2}{3}\)

\(\Leftrightarrow x=\frac{-3}{4}\)

\(\frac{2}{5}x+\frac{1}{2}=\frac{-3}{4}\)

\(\Leftrightarrow\frac{2}{5}x=\frac{-3}{4}-\frac{1}{2}\)

\(\Leftrightarrow\frac{2}{5}x=\frac{-5}{4}\)

\(\Leftrightarrow x=\frac{-5}{4}\div\frac{2}{5}\)

\(\Leftrightarrow x=\frac{-25}{8}\)

1) 4x-(2x-5)=21

4x-2x+5=21

2x+5=21

2x=21 -5

2x=16

x=16/2

x=8

2)14x+5=8x+10

14x-8x=10-5

6x=5

x=5/6

3) 15+5x=3x+30

5x-3x=30-15

2x=15

x=15/2

Vậy x=15/2

1.

Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{5}=\frac{y}{7}=\frac{z}{10}=\frac{2x}{10}=\frac{y}{7}=\frac{z}{10}$

$=\frac{2x+y-z}{10+7-10}=\frac{-21}{7}=-3$

$\Rightarrow x=-3.5=-15; y=-3.7=-21; z=-3.10=-30$

2.

Áp dụng tính chất dãy tỉ số bằng nhau:

$\frac{x}{3}=\frac{y}{4}=\frac{z}{6}=\frac{2x}{6}=\frac{4y}{16}=\frac{3z}{18}$

$=\frac{4y-2x+3z}{16-6+18}=\frac{-56}{28}=-2$

$\Rightarrow x=-2.3=-6; y=-2.4=-8; z=-2.6=-12$

5/2+x=-3/5

x=-3/5-5/2

x=-31/10

vậy x=-31/10

-2x+5=23

-2x=23-5

-2x=18

x=18:-2

x=-9

vậy x=-9

                                      Bài làm :

\(\frac{5}{2}+x=-3,5\)

\(\Leftrightarrow x=-3,5-\frac{5}{2}=-6\)

\(-2x+5=23\)

\(\Leftrightarrow-2x=18\)

\(\Leftrightarrow x=-9\)

\(\frac{x}{21}=\frac{2}{7}-\frac{4}{3}\)

\(\Leftrightarrow\frac{x}{21}=-\frac{22}{21}\)

\(\Leftrightarrow x=-22\)

\(\frac{5}{3}x-\frac{2}{5}x=\frac{19}{10}\)

\(\Leftrightarrow x\left(\frac{5}{3}-\frac{2}{5}\right)=\frac{19}{10}\)

\(\Leftrightarrow\frac{19}{15}x=\frac{19}{10}\)

\(\Leftrightarrow x=\frac{3}{2}\)

Chúc bạn học tốt !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

x/21=2/7-4/3

x/21=-22/21

x×21=21×-22

x×21=-462

x=-462:21

x=22

vậy x=22

a: Ta có: \(\left|\dfrac{2}{5}-x\right|+\dfrac{1}{2}=3.5\)

\(\Leftrightarrow\left|x-\dfrac{2}{5}\right|=3\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{2}{5}=3\\x-\dfrac{2}{5}=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{17}{5}\\x=-\dfrac{13}{5}\end{matrix}\right.\)

b: Ta có: \(\dfrac{21}{5}+3:\left|\dfrac{x}{4}-\dfrac{2}{3}\right|=6\)

\(\Leftrightarrow3:\left|\dfrac{1}{4}x-\dfrac{2}{3}\right|=6-\dfrac{21}{5}=\dfrac{9}{5}\)

\(\Leftrightarrow\left|\dfrac{1}{4}x-\dfrac{2}{3}\right|=\dfrac{5}{3}\)

\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{4}x-\dfrac{2}{3}=\dfrac{5}{3}\\\dfrac{1}{4}x-\dfrac{2}{3}=-\dfrac{5}{3}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{4}x=\dfrac{7}{3}\\\dfrac{1}{4}x=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{28}{3}\\x=-4\end{matrix}\right.\)

1)6x-8=3x+1

6x-3x=1+8

3x=9

x=3

Vậy x=3

2: 12-10x=25-30x

=>20x=13

=>x=13/20

3: \(3\left(2x+3\right)-2\left(4x-5\right)=10x+21\)

=>6x+9-8x+10=10x+21

=>10x+21=-2x+19

=>12x=-2

=>x=-1/6

4: \(\Leftrightarrow25x-15-6x+12=11-5x\)

=>19x-3=11-5x

=>24x=14

=>x=7/12

5: \(\Leftrightarrow8-12x-5+10x=4-6x\)

=>4-6x=-2x+3

=>-4x=-1

=>x=1/4

6: \(\Leftrightarrow32x-24-6+9x=13-40x\)

=>41x-30=13-40x

=>81x=43

=>x=43/81

7: \(\Leftrightarrow10x-5+20x=5x-11\)

=>30x-5=5x-11

=>25x=-6

=>x=-6/25