ban lam sai rui de mk lam lai nhe.

\(12.\left(x-1\right):3=4^3-2^3\)

\(12.\left(x-1\right):3=64-8\)

\(12.\left(x-1\right):3=56\)

\(12.\left(x-1\right)=56.3\)

\(12.\left(x-1\right)=168\)

\(x-1=168:12\)

\(x-1=14\)

             \(x=15\)

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1: Ta có: \(\dfrac{x+4}{4}+\dfrac{3x-7}{5}=\dfrac{7x+2}{20}\)

\(\Leftrightarrow5x+20+12x-28=7x+2\)

\(\Leftrightarrow17x-7x=2+8=10\)

hay x=1

2: Ta có: \(\dfrac{x}{6}+\dfrac{1-3x}{9}=\dfrac{-x+1}{12}\)

\(\Leftrightarrow\dfrac{6x}{36}+\dfrac{4\left(1-3x\right)}{36}=\dfrac{3\left(-x+1\right)}{36}\)

\(\Leftrightarrow6x+4-12x=-3x+3\)

\(\Leftrightarrow-6x+3x=3-4\)

hay \(x=\dfrac{1}{3}\)

3: Ta có: \(\dfrac{x-3}{3}-\dfrac{x+2}{12}=\dfrac{2x-1}{4}\)

\(\Leftrightarrow4x-12-x-2=6x-3\)

\(\Leftrightarrow3x-14-6x+3=0\)

\(\Leftrightarrow-3x=11\)

hay \(x=-\dfrac{11}{3}\)

4: Ta có: \(\dfrac{x-2}{4}-\dfrac{2x+3}{3}=\dfrac{x+6}{12}\)

\(\Leftrightarrow3x-6-8x-12=x+6\)

\(\Leftrightarrow-5x-x=6+18\)

hay x=-4

5: Ta có: \(\dfrac{2x-1}{12}-\dfrac{3-x}{18}=\dfrac{-1}{36}\)

\(\Leftrightarrow6x-3+2x-6=-1\)

\(\Leftrightarrow8x=8\)

hay x=1

Chọn B

Đáp án là B vì 12: -3 = -4; 12: -4 = -3; 12: -6 = -2;12: -12 = -1 và đáp ứng điều kiện a< -2

Chọn A

\(a.\dfrac{3}{2}+\dfrac{-1}{3}< \dfrac{x}{6}< \dfrac{1}{9}+\dfrac{31}{18}\)

\(\Leftrightarrow\dfrac{7}{6}< \dfrac{x}{6}< \dfrac{11}{6}\)

\(\Leftrightarrow7< x< 11\)

\(\Leftrightarrow x\in\left\{8;9;10\right\}\)

\(b.\dfrac{-5}{12}+\dfrac{7}{12}+\dfrac{-1}{12}< \dfrac{x}{12}< \dfrac{2}{15}+\dfrac{1}{5}\)

\(\Leftrightarrow\dfrac{1}{12}< \dfrac{x}{12}< \dfrac{1}{3}\)

\(\Leftrightarrow\dfrac{1}{12}< \dfrac{x}{12}< \dfrac{4}{12}\)

\(\Leftrightarrow1< x< 4\)

\(\Leftrightarrow x\in\left\{2;3\right\}\)

Bn cộng 2 phân số đó lại

1.a,=(54+45+1).113

=100.113

=11300

b,=(3/7+8/14)+(4/9+10/18)

=1+1

=2

2.a,=13/10+1/3

=49/30

b,=12/9.(1/12+1/6)

=12/9.1/4

=1/3

c,=3/4.3/2

=9/8

d,=3/2-1/3

=7/6

1:tính bằng cách thuận tiện nhất:

a)54 x 113 + 45 x 113 + 113

= 54 x 113 + 45 x 113 + 113x1

=113 x(54+45+1)

= 113x100

=1300

 b)3/7 + 4/9 + 8/14 + 10/18

=(3/7+8/14)+(4/9+10/18)

=    1           + 1

=2

bài 1:

a) 1/3x=-5/3

x=-5

b) x+12/5=37/15

x=1/15

c) x-1/7=-36/7

x=-5

d) 3x-1/2=0

3x=1/2

x=1/6

e) 2/5+x=1/4

x=-3/20

Viết rõ ra hộ mình với

1/3x=4/3-3=-5/3

x=-5/3:1/3=-5

`(x+2)-2=0`

`=>x+2=0+2`

`=>x+2=2`

`=>x=2-2`

`=>x=0`

__

`(x+3)+1=7`

`=>x+3=7-1`

`=>x+3=6`

`=>x=6-3`

`=>x=3`

__

`(x+3)+4=12`

`=>x+3=12-4`

`=>x+3=8`

`=>x=8-3`

`=>x=5`

__

`(5x+4)-1=13`

`=>5x+4=13+1`

`=>5x+4=14`

`=>5x=14-4`

`=>5x=10`

`=>x=10:5`

`=>x=2`

__

`(4x-8)+3=12`

`=>4x-8=12-3`

`=>4x-8=9`

`=>4x=9+8`

`=>4x=17`

`=> x=17/4`

__

`3+(x-5)=14`

`=>x-5=14-3`

`=>x-5=11`

`=>x=11+5`

`=>x=16`