a) 7- x/12=1/2

     x/12=7-1/2

      x/12 =14/2-1/2

      x/12=13/2

       x/12=78/12

       x=78 

        vậy x=78

mình nhân cả tử và mẫu với 13/2 nên mới ra 78/12

21, -6x-(-7)=25

giúp mk vs nha

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

\(=>\left(7+x\right).3=2.12\)

\(=>21+3x=24\)

\(=>3x=3\)

\(=>x=1\)

vay \(x=1\)

\(\frac{25-x}{18}=\frac{1}{2}\)

\(=>\left(25-x\right).2=18\)

\(=>50-2x=18\)

\(=>-2x=32\)

\(=>x=-16\)

vay \(x=-16\)

7+x / 12 = 2 / 3

7 + x = 8

x = 1

25 - x / 18 = 1 /2

25 - x = 9

x = 16

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

\(=>21+3x=24\)

\(=>x=1\)

\(\frac{25-x}{18}=\frac{1}{2}\)

\(=>50-2x=18\)

\(=>-2x=50-18\)

\(=>-2x=32\)

\(=>x=-16\)

7+x/12=2/3

    x/12=7-2/3

    x/12=19/3

19/3=76/12

=>x=76   

25-x/18=1/2

     x/18=25-1/2

     x/18=49/2

49/2=441/18

=>x=441

7+x/12=2/3

    x/12=7-2/3

    x/12=19/3

19/3=76/12

=>x=76   

25-x/18=1/2

     x/18=25-1/2

     x/18=49/2

49/2=441/18

=>x=441

Bài 2: 

a: \(\left(6x-39\right):7=3\)

\(\Leftrightarrow6x-39=21\)

hay x=10

Ta có (7+x)/12=2/3

  suy ra 3(7+x)=24

  suy ra 7+x=8

          x=1

Ta có (25-x)/18=1/2

suy ra 2(25-x)=18

suy ra 25-x=9

         x=16

a,x=-76

b,x=441

1.\(7+\frac{x}{12}=\frac{2}{3}\)

\(\frac{x}{12}=\frac{2}{3}-7=-\frac{19}{3}\)

\(x=-\frac{19}{3}.12=-76\)

Vậy x=-76

2.\(25-\frac{x}{18}=\frac{1}{2}\)

\(\frac{x}{18}=25-\frac{1}{2}=\frac{49}{2}\)

\(x=\frac{49}{2}.18=441\)

Vậy x=441

a)x-3/4=5/12 : 10/3

x-3/4= 1/8

x = 1/8 + 3/4

x = 7/8

b)7/6 - x=3/5 x 15/18

7/6 - x = 1/2

x = 7/6 - 1/2

x = 2/3

a)x-3/4=5/12 : 10/3

x-3/4= 1/8

x = 1/8 + 3/4

x = 7/8

b)7/6 - x=3/5 x 15/18

7/6 - x = 1/2

x = 7/6 - 1/2

x = 2/3

a, \(\frac{7+x}{12}=\frac{2}{3}\)             

\(\frac{7+x}{12}=\frac{8}{12}\)

\(x=8-7\)

\(x=1\)