`a)(4,5-2x)*1 4/7=11/14`

`=>(4,5-2x)*11/7=11/14`

`=>4,5-2x=1/2`

`=>2x=4,5-0,5=4`

`=>x=2`

Vậy `x=2`

`b)(2,8x-32):2/3=-90`

`=>2,8x-32=-90*2/3=-60`

`=>2,8x=-28`

`=>x=-10`

Vậy `x=-10`

\(\left(2,8:x-32\right):\frac{2}{3}=-90\)

\(2,8:x-32=\left(-90\right).\frac{2}{3}\)

\(2,8:x-32=-60\)

\(2,8:x=-28\)

\(x=\left(-28\right):2,8\)

\(x=-10\)

\(4-\left|x-2012\right|=\left(-2\right)^2\)

\(4-\left|x-2012\right|=-4\)

\(\left|x-2012\right|=8\)

\(\Rightarrow\orbr{\begin{cases}\left|x-2012\right|=8\\\left|x-2012\right|=-8\end{cases}\Rightarrow\orbr{\begin{cases}x=2020\\x=2004\end{cases}}}\)

(2,8 . x - 32) : 2/3 = -90

(2,8 . x - 32) = -90 x 2/3

(2,8 . x - 32) = -60

2,8 . x = -60 + 32

2,8 . x = -28

x = -28 : 2,8

x = -10

`(2,8 . x - 32) : 2/3 = -90`

`(2,8 . x - 32) = -90 xx (-2/3)`

`2,8 . x = 60 + 32`

`2,8 . x = 92`

`x = 92 : 2,8`

`x = 92/2,8`

\(\left(2,8\cdot x-32\right):\dfrac{2}{3}=-90\)

\(\left(\dfrac{14}{5}\cdot x-32\right):\dfrac{2}{3}=-90\)

\(\dfrac{14}{5}\cdot x-32=\left(-90\right)\cdot\dfrac{2}{3}\)

\(\dfrac{14}{5}\cdot x-32=-60\)

\(\dfrac{14}{5}\cdot x=\left(-60\right)+32\)

\(\dfrac{14}{5}\cdot x=-28\)

        \(x=\left(-28\right):\dfrac{14}{5}\)

        \(x=\left(-28\right)\cdot\dfrac{5}{14}\)

        \(x=-10\)

( 2,8x - 32 ) : 2/3 = -90

 2,8x - 32           = -90.2/3

 2,8x - 32           = -60

 2.8x                  = -60+32

 2.8x                  = -28

     x                   = -10 

a) (2,8 . x -32) : 2/3 = -90

=>(2,8x-32):2/3=-90

=>21/5x-48=-90

=>21/5x=-42

=>x=-10

vậy x=-10

                                                                Bài giải

a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)

\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)

b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)

\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)

c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)

d,  \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)

\(=1+1+1\)

\(=3\)

e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)

\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)

\(=1+1+1\)

\(=3\)

a, \(\frac{4}{5}-\frac{2}{3}+\frac{1}{5}-\frac{1}{3}\)

\(=\left(\frac{4}{5}+\frac{1}{5}\right)-\left(\frac{2}{3}+\frac{1}{3}\right)=1-1=0\)

b, \(\frac{2}{5}\text{ x }\frac{7}{4}-\frac{2}{5}\text{ x }\frac{3}{7}\)

\(=\frac{2}{5}\text{ x }\left(\frac{7}{4}-\frac{3}{7}\right)=\frac{2}{5}\text{ x }\frac{37}{28}=\frac{37}{70}\)

c, \(\frac{13}{4}\text{ x }\frac{2}{3}\text{ x }\frac{4}{13}\text{ x }\frac{3}{12}=\frac{13\text{ x }2\text{ x }4\text{ x }3}{4\text{ x }3\text{ x }13\text{ x }12}=\frac{1}{6}\)

d,  \(\frac{75}{100}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\frac{3}{4}+\frac{18}{21}+\frac{19}{32}+\frac{1}{4}+\frac{3}{21}+\frac{13}{32}\)

\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{18}{21}+\frac{3}{21}\right)+\left(\frac{19}{32}+\frac{13}{32}\right)\)

\(=1+1+1\)

\(=3\)

e, \(\frac{2}{5}+\frac{6}{9}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{2}{5}+\frac{2}{3}+\frac{3}{4}+\frac{3}{5}+\frac{1}{3}+\frac{1}{4}\)

\(=\frac{1}{5}\left(2+3\right)+\frac{1}{3}\left(2+1\right)+\frac{1}{4}\left(3+1\right)\)

\(=\frac{1}{5}\cdot5+\frac{1}{3}\cdot3+\frac{1}{4}\cdot4\)

\(=1+1+1\)

\(=3\)

a ,            =(4/5+1/5)-(2/3+1/3)=1-1=0

  b   ,            =2/5 x (7/4-3/7) =2/5 x 37/28 =74/140=37/70

c,             =13/4 x 2/3 x 13/4  x 2/3=26/12 x 26/12= 13/6 x 13/6 =13 x 13/6 x 6(gạch 13 trên tử thì tử còn 1 x 13,mẫu hết.) =1 x 13/1=13

d,               =3/4+6/7+19/32 +1/4+1/7 +13/32=(3/4+1/4 )+(6/7+1/7)+(19/32+13/32)=1+1+1=3

e,            =(2/5+3/5)+(2/3+1/3)+(3/4+1/4) [6/9 rút gọn thành 2/3] =1+1+1=3

\(\frac{a}{27}=\frac{-5}{9}=\frac{-45}{b}\)

\(=>\frac{a.3}{81}=\frac{-45}{81}=\frac{-45}{b}\)

=>b=81

     a.3=-45

     a=-15

Vậy a=-15;b=81

(2,8.x-32):2/3=-90

=>2,8.x-32=90x2/3

=>2,8.x-32=60

=>2,8.x=60+32

=>2,8.x=92

=>x=92:2,8

=>x=230/7

( 2,8.x - 32 ) : \(\frac{2}{3}\) = - 90

= 2,8.x - 32 = 90. \(\frac{2}{3}\) 

= 2,8.x - 32 = 60

= 2,8.x = 60 + 32

= 2,8.x = 92

 x = 92 : 2,8 

 x = \(\frac{230}{7}\)

Vậy x bằng \(\frac{230}{7}\)