a. 3/7 - 1/2x = 5/3 

=>        1/2x = 3/7 -  5/3

=>         1/2x = 9/21 - 15/21

=>          1/2x = -26/21

=>               x = -26/21 : 1/2

=>               x = -26/21.2 

=>               x = -52/21

b. -2x + 3/14 = 1/7 - 4/21

  =>  -2x            = -3/14 + 1/7 - 4/21

  =>   -2x           = -18/84 + 12/84 - 16/84

  =>   -2x          = -22/84

 =>      x           = -22/84 : -2

 =>     x            = -22/84 . (-1/2) 

=>      x            = 11/84 

a. 3/7 - 1/2x = 5/3 

=>        1/2x = 3/7 -  5/3

=>         1/2x = 9/21 - 15/21

=>          1/2x = -26/21

=>               x = -26/21 : 1/2

=>               x = -26/21.2 

=>               x = -52/21

b. -2x + 3/14 = 1/7 - 4/21

  =>  -2x            = -3/14 + 1/7 - 4/21

  =>   -2x           = -18/84 + 12/84 - 16/84

  =>   -2x          = -22/84

 =>      x           = -22/84 : -2

 =>     x            = -22/84 . (-1/2) 

=>      x            = 11/84 

a)3x - 105 : 21 = 19

   3x - 5            = 19

   3x                  = 19 + 5

   3x                  = 24

     x                  = 24 : 8

     x                  = 3

b, x - 7 = 14 - 3 . 2³

    x - 7 = 14 - 3 . 8

    x - 7 = 14 - 24

    x - 7 = -10

    x      = (-10) + 7

    x      = -3

HT và $$$ 

Bài 2: 

a) 3x - 105 : 21= 19                                   b) x - 7= 14 - 3 . 2^3

   3x -   5          = 19                                       x - 7= 14 - 3.8

    3x                = 19+ 5                                  x - 7= 14 - 24

    3x                = 24                                        x - 7= -10

           x           = 24 : 3                                   x      = -10+7

           x           = 8                                          x      = -3

Bài 1:

a) \(\frac{16}{15}.\frac{\left(-5\right)}{14}.\frac{54}{24}.\frac{56}{21}\)

\(=\frac{4.2.2}{5.3}.\frac{\left(-5\right)}{2.7}.\frac{3.3}{4}.\frac{8}{3}\)

\(=\frac{4.2.2.\left(-5\right).3.3.8}{5.3.2.7.4.3}\)

\(=\frac{-16}{7}\)

b) \(\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{15}{21}.\frac{4}{\left(-5\right)}\)

\(=\frac{7}{3}.\frac{\left(-5\right)}{2}.\frac{5}{7}.\frac{2.2}{\left(-5\right)}\)

\(=\frac{7.\left(-5\right).5.2.2}{3.2.7.\left(-5\right)}\)

\(=\frac{10}{3}\)

Bài 2:

a) \(\frac{21}{24}.\frac{11}{9}.\frac{5}{7}=\frac{7}{8}.\frac{11}{9}.\frac{5}{7}=\frac{11.5}{8.9}=\frac{55}{72}\)

b) \(\frac{5}{23}.\frac{17}{26}+\frac{5}{23}.\frac{9}{26}\)

\(=\frac{5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{5}{23}.1=\frac{5}{23}\)

c) \(\left(\frac{3}{29}-\frac{1}{5}\right).\frac{29}{3}=\frac{3}{29}.\frac{29}{3}-\frac{1}{5}.\frac{29}{3}\)

\(=1-1\frac{14}{15}=\frac{14}{15}\)

Bài 3:

a) x/5 = 2/5

=> x =2

b) -4/x = 20/14 = 10/7

=> -4/x = 10/7

=> x.10 = (-4).7

x.10 = - 28

x= -28 :10

x= -2,8

c) 4/7 = 12/x = 12/ 21

=> 12/x = 12/21

=> x = 21

d) 3/7 = x / 21 = 9/21

=> x/21 = 9/21

=> x= 9

x/3=-14/21

=>x=3*(-14)/21=-2

Vậy x=-2

a) đề kiểu gì vậy bạn 

b) \(x+\frac{2}{14}=\frac{3}{21}\Leftrightarrow x=0\)

c) \(x+\frac{2}{7}=\frac{1}{2}\Leftrightarrow x=\frac{3}{14}\)

d) \(\frac{12}{15}=\frac{x-5}{10}\Leftrightarrow15x-75=120\Leftrightarrow15x=195\Leftrightarrow x=13\)

Bn  ơi phần a x đâu zùi?

a)x/10=-3/15

nhầm nha!

b) \(xy+3x-2y=11\)

\(xy+3x-2y-6=11-6\)

\(xy+3x-2y-6=5\)

\(\left(xy+3x\right)-\left(2y+6\right)=5\)

\(x\left(y+3\right)-2\left(y+3\right)=5\)

\(\left(x-2\right)\left(y+3\right)=5\)

\(\Rightarrow5=\left(-1\right)\left(-5\right)=1\cdot5\)

Bạn tự lập bảng mà thử nghiệm nhé

Ngu vcl

a) \(xy+3x-7y=21\)

\(xy+3x-7y-21=21-21\)

\(xy+3x-7y-21=0\)

\(\left(xy+3x\right)-\left(7y+21\right)=0\)

\(x\left(y+3\right)-7\left(y+3\right)=0\)

\(\left(x-7\right)\left(y+3\right)=0\)

\(\orbr{\begin{cases}x-7=0\\y+3=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=7\\y=-3\end{cases}}\)

=> x=-21.-6:14=9

Vậy x=9

Ta có: (-6).(-21)=14x

=> x= \(\dfrac{126}{14}\)=9

Vậy x=9

ĐKXĐ: \(x\ne0\)

Ta có: \(\dfrac{-6}{x}=\dfrac{14}{-21}\)

\(\Leftrightarrow x=\dfrac{\left(-6\right)\cdot\left(-21\right)}{14}=\dfrac{126}{14}=9\)(thỏa ĐK)

Vậy: x=9

kết quả là đéo biết 

k cho tao

\(-\frac{3}{7}\left(x-7\right)-\left(-\frac{5}{14}\right)\left(2x-3\right)-15=\frac{7}{-21}\)

\(\Leftrightarrow-\frac{3}{7}\left(x-7\right)+\frac{5}{14}\left(2x-3\right)=\frac{44}{3}\)

\(\Leftrightarrow-\frac{3}{7}x+3+\frac{5}{7}x-\frac{15}{14}=\frac{44}{3}\)

\(\Leftrightarrow x\left(-\frac{3}{7}+\frac{5}{7}\right)+3-\frac{15}{14}=\frac{44}{3}\)

\(\Leftrightarrow x\frac{2}{7}+3=\frac{661}{42}\)

\(\Leftrightarrow x\frac{2}{7}=\frac{535}{42}\Leftrightarrow x=\frac{535}{12}\)