a, 3/4 + 1/4.x=2

    1/4.x        = 2-3/4

     1/4.x      =5/4

     x           = 5/4:1/4

     x           = 5

b, x-2/3.9/4=2,5-1/2

    x-2/3.9/4=2

    x-2/3     =2:9/4

    x-2/3   =8/9

     x        = 8/9+2/3

     x         = 14/9

đặt 1/2 ra 

phần mẫu áp dụng công thức tính tổng còn lại tự làm nhoa bé

\(1\frac{2}{24}\times5\frac{2}{5}\times2\times3\frac{7}{9}\times2\)x2/17

\(=\frac{26}{24}\times\frac{27}{5}\times2\times\frac{34}{9}\times2\times\frac{2}{17}\)

\(=\frac{351}{60}\times2\times\frac{34}{9}\times2\times\frac{2}{17}\)

\(=\frac{351}{30}\times\frac{34}{9}\times2\times\frac{2}{17}\)

\(=\frac{5967}{135}\times2\times\frac{2}{17}\)

\(=\frac{11934}{135}\times\frac{2}{17}\)

\(=\frac{2652}{255}\)

a)\(\frac{2}{3}\cdot x+\frac{1}{4}=\frac{5}{6}\)

\(\frac{2}{3}\cdot x=\frac{5}{6}-\frac{1}{4}=\frac{7}{12}\)

\(x=\frac{7}{12}:\frac{2}{3}=\frac{7}{8}\)

b) \(\frac{7}{12}-\frac{5}{6}\cdot x=\frac{1}{4}:\frac{2}{3}\)

\(\frac{7}{12}-\frac{5}{6}\cdot x=\frac{3}{8}\)

\(\frac{5}{6}\cdot x=\frac{7}{12}-\frac{3}{8}=\frac{5}{24}\)

\(x=\frac{5}{24}:\frac{5}{6}=\frac{1}{4}\)

c) \(2\frac{1}{3}-\left(x+1\right)=\frac{5}{9}\)

\(\frac{7}{3}-\left(x+1\right)=\frac{5}{9}\)

\(x+1=\frac{7}{3}-\frac{5}{9}=\frac{16}{9}\)

\(x=\frac{16}{9}-1=\frac{7}{9}\)

d) \(\frac{2\cdot x+1}{15}=\frac{3}{5}\)

\(\left(2\cdot x+1\right):15=\frac{3}{5}\)

\(2\cdot x+1=\frac{3}{5}\cdot15=9\)

\(2\cdot x=9-1=8\)

\(x=8:2=4\)

a, 2/3 . x +1/4=5/6

      2/3 . x=5/6-1/4

      2/3 . x=10/12 -3/12

       2/3 . x=7/12

       x= 7/12 : 2/3

      x=7/8 

Vậy x=7/8

`1/2 xx x +3/2 =7`

`=> 1/2 xx x = 7-3/2`

`=> 1/2 xx x = 14/2 -3/2`

`=> 1/2 xx x = 11/2`

`=> x= 11/2 :1/2`

`=> x=11/2 xx2`

`=> x= 22/2`

`=>x=11`

Vậy `x=11`

__

`3/2 xx x -2/7 xx(x-7/2)=18`

`=> 3/2 xx x -2/7x + 1=18`

`=> (3/2 -2/7 )x+ 1 =18`

`=> 17/14 x=18-1`

`=> 17/14x=17`

`=>x=17:17/14`

`=> x=17 xx 14/17`

`=>x=14`

a) \(\dfrac{1}{2}\times x+\dfrac{3}{2}=7\)

\(\dfrac{1}{2}\times x=7-\dfrac{3}{2}\)

\(\dfrac{1}{2}\times x=\dfrac{11}{2}\)

\(x=\dfrac{11}{2}\div\dfrac{1}{2}\\ x=\dfrac{11}{2}\times2\\ x=\dfrac{22}{2}=11\)

b) \(\dfrac{3}{2}\times x-\dfrac{2}{7}\times\left(x-\dfrac{7}{2}\right)=18\)

\(\dfrac{3}{2}\times x-\left(\dfrac{2}{7}x-1\right)=18\)

\(\dfrac{3}{2}\times x-\dfrac{2}{7}x+1=18\)

\(\dfrac{3}{2}x-\dfrac{2}{7}x+1=18\)

\(\dfrac{17}{14}x+1=18\)

\(\dfrac{17}{14}x=18-1\)

\(\dfrac{17}{14}x=17\)

\(x=17\div\dfrac{17}{14}\)

\(x=17\times\dfrac{14}{17}\)

\(x=14\)