a: x*3/4=1/5

=>x=1/5:3/4=1/5*4/3=4/15

b: x*3/7=2/5

=>x=2/5:3/7=2/5*7/3=14/15

c: 1/3+2/9=2/12x

=>1/6x=3/9+2/9=5/9

=>x=5/9*6=30/9=10/3

d: 4/15*x-2/3=1/5

=>4/15*x=2/3+1/5=10/15+3/15=13/15

=>4x=13

=>x=13/4

e: x:1/7=2/3

=>x=2/3*1/7=2/21

f: 1/9:x=7/3

=>x=1/9:7/3=1/9*3/7=3/63=1/21

j: 1/4+5/12=8/3:x

=>8/3:x=3/12+5/12=8/12=2/3

=>x=4

h: =>7/4:x=1/5+1/2=7/10

=>x=7/4:7/10=10/4=5/2

a) 4.25-12.5+170:10

=100-60+17

=40+17

=57

b) (7+3³:3²).4-3

=(7+3).4-3

=10.4-3

=40-3

=37

c) 12:{400:[500-(125+25.7)]}

=12:{400:[500-(125+175)]}

=12:{400:[500-300]}

=12:{400:200}

=12:2

=6

d) 168+{[2.(2⁴+3²)-256⁰]:7²}

=168+{[2.(16+9)-1]:49}

=168+{[2.25-1]:49}

=168+{[50-1]:49}

=168+{49:49}

=168+1

=169

A

A

A

\(=\dfrac{7}{12}\times\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{7}{12}\times\dfrac{7}{7}=\dfrac{7}{12}\)

`7/12xx3/7+7/12xx4/7=7/12xx(3/7+4/7)=7/12xx7/7=7/12`

\(\dfrac{7}{12}.\dfrac{3}{7}+\dfrac{7}{12}.\dfrac{4}{7}=\dfrac{7}{12}\left(\dfrac{3}{7}+\dfrac{4}{7}\right)=\dfrac{7}{12}\)

\(a,-5.\left(-x+7\right)-3.\left(-x-5\right)=-4.\left(12-x\right)+48\)

                          \(5x-35-3x+15=-48+4x+48\)

                                                \(2x-10=4x\)

                                                \(2x-4x=10\)

                                                       \(-2x=10\)

                                                             \(x=-5\)

 \(b,\left(-x-7\right)-5.\left(-x-3\right)=12.\left(3-x\right)\)

                  \(-x-7+5x+15=36-12x\)

                                         \(4x+8=36-12x\)

                                    \(4x+12x=36-8\)

                                               \(16x=28\)

                                                    \(x=1,75\)

các câu còn lại tương tự nha

`3/5 : x =1/3 +1/2`

` 3/5 : x= 2/6 +3/6`

` 3/5 : x= 5/6`

` x= 3/5 : 5/6`

` x= 3/5 xx 6/5`

` x= 18/25`

__

`x: 7/15 =2`

` x= 2xx 7/15`

` x= 14/15`

__

`x-3/2=11/4-5/4`

`x-3/2= 6/4`

`x= 3/2 +3/2`

`x= 6/2`

`x=3`

__

`x+5/4 = 3/2+7/12`

`x+5/4 = 18/12+7/12`

`x+5/4 = 25/12`

`x= 25/12-5/4`

`x= 25/12- 15/12`

`x= 10/12`

`x= 5/6`

Bài 1: 

a: -8/12<0<-3/-4

b: -56/24<0<7/3

c: 4/25<1<15/13

=>-4/25>-15/13

Bài 2: 

a: =-60/45=-4/3

b: =4/15-3/2-8/5=8/30-45/30-48/30=-85/30=-17/6

a ) \(-5\times\left(-x+7\right)-3\times\left(-x-5\right)=-4\times\left(12-x\right)+48\)

\(\Leftrightarrow5x-35+3x+15=-48+4x+48\)

\(\Leftrightarrow5x-3x+4x=35-15-48+48\)

\(\Leftrightarrow2x=20\)

\(\Leftrightarrow x=10\)

b ) \(-2\times\left(15-3x\right)-4\times\left(-7x+8\right)=-5-9\times\left(-2x+1\right)\)

\(\Leftrightarrow-30+6x-28x-32=-5+18x-9\)

\(\Leftrightarrow6x-28x-18x=30+32-5-9\)

\(\Leftrightarrow-40x=48\)

\(\Leftrightarrow x=-1.2\)

C,D nưã bạn

 c, 7 . ( - x - 7 ) - 5 . ( - x - 3 ) = 12 . ( 3 - x)

<=> - 7x - 49  + 5x  + 15 = 36 - 12x

<=>  - 2x + 12x = 36 - 15 + 49

<=> 10 x = 70

<=> x = 7

Vẫy  x = 7

d, 5 . ( - 3x - 7 ) - 4 . ( - 2x - 11 ) = 7 . ( 4x + 10) + 9

<=> - 15x + 8x + 44 = 28x + 70 + 9

<=> - 7x + 44 = 28x + 79

<=> - 7x - 28x = 79 - 44

<=> - 35x = 35

<=> x = - 1

Vậy x = - 1

Hc tốt

ĐKXĐ:\(x\ne3,4,7,12\)

\(\dfrac{1}{\left(x-3\right)\left(x-4\right)}+\dfrac{3}{\left(x-4\right)\left(x-7\right)}+\dfrac{5}{\left(x-7\right)\left(x-12\right)}=\dfrac{1}{4}\\ \Leftrightarrow\dfrac{1}{x-3}-\dfrac{1}{x-4}+\dfrac{1}{x-4}-\dfrac{1}{x-7}+\dfrac{1}{x-7}-\dfrac{1}{x-12}=\dfrac{1}{4}\\ \Leftrightarrow\dfrac{1}{x-3}-\dfrac{1}{x-12}=\dfrac{1}{4}\\ \Leftrightarrow\dfrac{x-12-x+3}{\left(x-3\right)\left(x-12\right)}=\dfrac{1}{4}\\ \Leftrightarrow\dfrac{-9}{x^2-15x+36}=\dfrac{1}{4}\\ \Leftrightarrow x^2-15x+36=-36\\ \Leftrightarrow x^2-15x+72=0\)

\(\Leftrightarrow x^2-2.\dfrac{15}{2}x+\dfrac{225}{4}+\dfrac{63}{4}=0\\ \Leftrightarrow\left(x-\dfrac{15}{2}\right)^2+\dfrac{63}{4}=0\left(vô.lí\right)\)

\(\Leftrightarrow\dfrac{1}{x-3}-\dfrac{1}{x-4}+\dfrac{1}{x-4}-\dfrac{1}{x-7}+\dfrac{1}{x-7}-\dfrac{1}{x-12}=\dfrac{1}{4}\)

\(\Leftrightarrow\dfrac{1}{x-3}-\dfrac{1}{x-12}=\dfrac{1}{4}\)

\(\Leftrightarrow\dfrac{x-12-x+3}{\left(x-3\right)\left(x-12\right)}=\dfrac{1}{4}\)

\(\Leftrightarrow\left(x-3\right)\left(x-12\right)=-36\)

=>x(x-15)=0

=>x=0 hoặc x=15

1) 3(x - 4) - (8 - x) = 12

3x - 12 - 8 + x = 12

4x - 20 = 12

4x = 12 + 20

4x = 32

x = 8

2) 5(x - 6) - 2(x + 3) = 12

5x - 30 - 2x - 6 = 12

3x - 36 = 12

3x = 12 + 36

3x = 48

x = 16

3) 5 - | x + 7| = 4

|x + 7| = 4 - 5

1, \(3.\left(x-4\right)-\left(8-x\right)=12\)

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

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

\(\Leftrightarrow4x=32\)

\(\Leftrightarrow x=8\)

​​Vậy : \(x=8\)

2, \(5.\left(x-6\right)-2.\left(x+3\right)=12\)

\(\Leftrightarrow5x-30-2x-6=12\)

\(\Leftrightarrow5x-2x=12+30+6\)

\(\Leftrightarrow3x=48\)

\(\Leftrightarrow x=\frac{48}{3}=16\)

Vậy : \(x=16\)

3, \(5-\left|x+7\right|=4\)

\(\Leftrightarrow\left|x+7\right|=5-4=1\)

\(\Leftrightarrow\left[{}\begin{matrix}x+7=1\\x+7=-1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-8\end{matrix}\right.\)

Vậy : \(x\in\left\{6,-8\right\}\)

4, \(6.\left|x-7\right|=18:\left(-3\right)\)

\(\Leftrightarrow6.\left|x-7\right|=-6\)

\(\Leftrightarrow\left|x-7\right|=-1\)

Ta thấy : \(\left|x-7\right|\ge0\forall x\) mà \(-1< 0\)

\(\Rightarrow x\in\varnothing\)

Vậy : không có \(x\) thỏa mãn đề.