Bài 1 :

\(a)x=\frac{7}{25}+\left(-\frac{1}{5}\right)\)

    \(x=\frac{2}{25}\)

\(b)x=\frac{5}{11}+\left(\frac{4}{-9}\right)\)

    \(x=\frac{1}{99}\)

Mấy câu kia dễ tự làm :>

Bài làm:

a) \(\frac{x}{3}=\frac{2}{3}+\left(-\frac{1}{7}\right)\)

<=>\(\frac{x}{3}=\frac{2.7-1.3}{3.7}\)

<=>\(\frac{x}{3}=\frac{11}{21}\)

<=> \(21.x=33\)

<=> \(x=\frac{11}{7}\)

b) \(x-\frac{1}{4}=\frac{2}{13}\)

<=> \(x=\frac{1}{4}+\frac{2}{13}\)

<=> \(x=\frac{13.1+2.4}{4.13}\)

<=> \(x=\frac{21}{52}\)

c)\(\frac{4}{7}.x=\frac{9}{8}-\frac{125}{1000}\)

<=> \(\frac{4}{7}.x=\frac{9}{8}-\frac{1}{8}\)

<=> \(\frac{4}{7}.x=\frac{8}{8}\)

<=> \(x=1:\frac{4}{7}\)

<=> \(x=\frac{7}{4}\)

Học tốt!!!!

7 + 67 + 56 - 76 + 368 -  93 + 45 -88 =

 =?      ?      ?     ?        ?       ?     ?

=        ?            ?          ?       ?        ?

=   ?

Bài 1

a) (3x - 2⁴).7³ = 2.7⁴

3x - 16 = 2.7⁴ : 7³

3x - 16 = 2.7

3x - 16 = 14

3x = 14 + 16

3x =30

x = 30 : 3

x = 10

b) x - [42 + (-28)] = -8

x - 14 = -8

x = -8 + 14

x = 6

c) 4 - 7.x = x - (13 - 4)

x + 7x = 4 + 9

8x = 13

x = 13/8

Bài 1: a,   (3\(x\) - 2⁴ ).7³ = 2.7⁴

                3\(x\) - 2⁴    = 2.7⁴ : 7³

                3\(x\)  - 16   = 14

                 3\(x\)           = 30 

                    \(x\)          = 10

b, \(x\) - (42 + (-28) ] = -8

    \(x\) - 14 = -8

    \(x\)        = 14 - 8

    \(x\)        = 6

c, 4 - (7\(x\)) = \(x\) - (13 - 4)

   4 - 7\(x\)   = \(x\) - 9

        \(x\) + 7\(x\) = 4 + 9

          8\(x\)     = 13

             \(x\)    = \(\dfrac{13}{8}\)

\(a,\dfrac{2}{3}.x=\dfrac{2}{7}\\ x=\dfrac{2}{7}:\dfrac{2}{3}=\dfrac{3}{7}\\ ---\\ b,x.\dfrac{3}{5}=\dfrac{2}{5}\\ x=\dfrac{2}{5}:\dfrac{3}{5}=\dfrac{2}{3}\\ ---\\ c,x:\dfrac{8}{13}=\dfrac{13}{7}\\x=\dfrac{13}{7}.\dfrac{8}{13}=\dfrac{8}{7}\\ ----\\ d,\dfrac{3}{2}:x=\dfrac{7}{4}\\ x=\dfrac{3}{2}:\dfrac{7}{4}=\dfrac{3}{2}.\dfrac{4}{7}=\dfrac{6}{7}\)

a: \(=\dfrac{-3}{5}\cdot\dfrac{5}{7}+\dfrac{-3}{5}\cdot\dfrac{3}{7}+\dfrac{-3}{5}\cdot\dfrac{6}{7}\)

\(=\dfrac{-3}{5}\left(\dfrac{5}{7}+\dfrac{3}{7}+\dfrac{6}{7}\right)=\dfrac{-3}{5}\cdot2=-\dfrac{6}{5}\)

b: \(=\dfrac{3}{13}\cdot\dfrac{6}{11}+\dfrac{3}{13}\cdot\dfrac{5}{11}-\dfrac{2}{13}=\dfrac{3}{13}-\dfrac{2}{13}=\dfrac{1}{13}\)

c: =>1/2x+1+3/8=7/16

=>1/2x=-15/16

=>x=-15/8

d: =>5/2x-1/3=1/6*(-9)/2=-9/12=-3/4

=>5/2x=-3/4+1/3=-9/12+4/12=-5/12

=>x=-1/6

cau b là sao bn

Bài 13: 

a: =>20-x=15-8+13=20

hay x=0

Bài 1:

a: \(x=\dfrac{2}{3}:\dfrac{3}{5}=\dfrac{2}{3}\cdot\dfrac{5}{3}=\dfrac{10}{9}\)

b: \(x=\dfrac{17}{8}:\dfrac{7}{17}=\dfrac{17}{8}\cdot\dfrac{17}{7}=\dfrac{289}{56}\)

c: \(x=-\dfrac{3}{4}:\dfrac{7}{12}=\dfrac{-3}{4}\cdot\dfrac{12}{7}=\dfrac{-63}{28}=-\dfrac{9}{4}\)

d: \(\Leftrightarrow x\cdot\dfrac{1}{6}=\dfrac{3}{8}-\dfrac{1}{4}=\dfrac{1}{4}\)

hay \(x=\dfrac{1}{4}:\dfrac{1}{6}=\dfrac{3}{2}\)

e: \(\Leftrightarrow\dfrac{1}{2}:x=-4-\dfrac{1}{3}=-\dfrac{17}{3}\)

hay \(x=-\dfrac{1}{2}:\dfrac{17}{3}=\dfrac{-3}{34}\)

dad

Bài 1: Tìm \(x\) 

a; \(x-2\) + 7 = 1.3.(-9)

   \(x\) - 2 + 7 = 3.(-9)

   \(x\) - 2 + 7 = - 27

  \(x\)             = - 27 - 7 + 2

   \(x\)            = - 34 + 2

   \(x\)            = - 32

Vậy \(x=-32\)

Bài 1

c; - 2\(x\) + 5 = 7

     - 2\(x\)       = 7  - 5

    - 2\(x\)        = - 2

        \(x\)        = -2 : (-2)

        \(x\)        = - 1

Vậy \(x\)         = - 1

Bai 2 : 

\(\hept{\begin{cases}x+y=7\\x-7=13\end{cases}\Leftrightarrow\hept{\begin{cases}x+y=7\\x=20\end{cases}}}\)

Thay x vào phương trình đầu ta có : 

\(20+y=7\Leftrightarrow y=-13\)

Vậy \(\left\{x;y\right\}=\left\{20;-13\right\}\)

Thử \(20-13=7\); \(20-7=13\)( thỏa mãn )