a: =>x=76545:243=315

b: =>x=97328:316=308

=>x=76545:243=315

=>x=97328:316=308

a: =>136,5-x=6,48

=>x=130,02

b: =>259,2:x=43,2

=>x=6

a/ 136,5 –x = 5 ,4 x 1,2               

    136,5 - x = 6,48

                x = 136,5 - 6,48

                x = 130,02

b/ 259,2 : x = 39 + 4,2    

    259,2 : x = 43,2

                x = 259,2 : 43,2

                x = 6

`x+2/5=4/3`

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

`=> x= 20/15 -6/15`

`=>x= 14/15`

__

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

`=> x : 3/2= 2/5`

`=> x= 2/5 xx 3/2`

`=> x= 6/10`

`=>x= 3/5`

__

Bài `5` này có `1` chút lạ ạ 

3/5 * x -1/2 = 1/5

a) x = 9867655 - 456788 

x = 9410867

b) x = 9886 + 23345 

x = 33231

c) x = 986352 - 283476 

x = 702876

d) y =44772 : 123

y = 364

e) a = 2345 x 637

a = 1493765

g) x = 212552 : 326 

x = 652

Bài 2. Tìm x:

a/ x + 456788 = 9867655

    x                  =  9867655 -456788 

    x                  = 9410867

b/ x – 23345 = 9886

    x                = 9886 + 23345

     x                =33231

c/ 283476 + x = 986352

                    x =  986352 -  283476

                    x=     702876

d/ y × 123 = 44772

    y            = 44772 : 123 

     y           = 364

e/ a : 637 = 2345

    a          = 2345 x 637

    a          =   1493765

g/ 212 552 : x = 326

                    x = 212 552 : 326 

                    x  = 652

h/ 40000 – x =3876

                  x = 40000 – 3876

                  x = 36124

i/ (x + 1233) – 1978 = 9876

    x + 1233               = 9876 + 1978

    x + 1233               = 11854

k/ x : 2 : 3 = 138

    x : 2       = 138 x 3 

    x : 2       =414

    x             = 414 x 2

     x             = 828

Bài 4: 

a) \(\dfrac{4}{3}+\left(1,25-x\right)=2,25\)

\(1,25-x=2,25-\dfrac{4}{3}=\dfrac{9}{4}-\dfrac{4}{3}\)

\(1,25-x=\dfrac{11}{12}\)

\(x=1,25-\dfrac{11}{12}=\dfrac{5}{4}-\dfrac{11}{12}\)

\(x=\dfrac{1}{3}\)

b) \(\dfrac{17}{6}-\left(x-\dfrac{7}{6}\right)=\dfrac{7}{4}\)

\(x-\dfrac{7}{6}=\dfrac{17}{6}-\dfrac{7}{4}=\dfrac{34}{12}-\dfrac{21}{12}\)

\(x-\dfrac{7}{6}=\dfrac{13}{12}\)

\(x=\dfrac{13}{12}+\dfrac{7}{6}=\dfrac{13}{12}+\dfrac{14}{12}\)

\(x=\dfrac{27}{12}=\dfrac{9}{4}\)

c) \(4-\left(2x+1\right)=3-\dfrac{1}{3}=\dfrac{9}{3}-\dfrac{1}{3}\)

\(4-\left(2x+1\right)=\dfrac{8}{3}\)

\(2x+1=\dfrac{8}{3}+4=\dfrac{8}{3}+\dfrac{12}{3}\)

\(2x+1=\dfrac{20}{3}\)

\(2x=\dfrac{20}{3}-1=\dfrac{20}{3}-\dfrac{3}{3}\)

\(2x=\dfrac{17}{3}\)

\(x=\dfrac{17}{3}.\dfrac{1}{2}=\dfrac{17}{6}\)

Bài 15:

a) \(\left(\dfrac{-2}{3}\right)^9:x=\dfrac{-2}{3}\)

\(x=\left(\dfrac{-2}{3}\right)^9:\dfrac{-2}{3}=\left(\dfrac{-2}{3}\right)^{9-1}\)

\(=>x=\left(\dfrac{-2}{3}\right)^8\)

b) \(x:\left(\dfrac{4}{9}\right)^5=\left(\dfrac{4}{9}\right)^4\)

\(x=\left(\dfrac{4}{9}\right)^4.\left(\dfrac{4}{9}\right)^5=\left(\dfrac{4}{9}\right)^{4+5}\)

\(=>x=\left(\dfrac{4}{9}\right)^9\)

c) \(\left(x+4\right)^3=-125\)

\(\left(x+4\right)^3=\left(-5\right)^3\)

\(=>x+4=-5\)

\(x=-5-4\)

\(=>x=-9\)

d) \(\left(10-5x\right)^3=64\)

\(\left(10-5x\right)^3=4^3\)

\(=>10-5x=4\)

\(5x=10-4\)

\(5x=6\)

\(=>x=\dfrac{6}{5}\)

e) \(\left(4x+5\right)^2=81\)

\(\Leftrightarrow\left[{}\begin{matrix}\left(4x+5\right)^2=\left(-9\right)^2\\\left(4x+5\right)^2=9^2\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}4x+5=-9\\4x+5=9\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}4x=-14\\4x=4\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-14}{4}\\x=1\end{matrix}\right.\)

Bài 16:

a) \(4-1\dfrac{2}{5}-\dfrac{8}{3}\)

\(=4-\dfrac{7}{5}-\dfrac{8}{3}\)

\(=\dfrac{60-21-40}{15}=\dfrac{-1}{15}\)

b) \(-0,6-\dfrac{-4}{9}-\dfrac{16}{15}\)

\(=\dfrac{-3}{5}+\dfrac{4}{9}-\dfrac{16}{15}\)

\(=\dfrac{\left(-27\right)+20-48}{45}=\dfrac{-55}{45}=\dfrac{-11}{9}\)

c) \(-\dfrac{15}{4}.\left(\dfrac{-7}{15}\right).\left(-2\dfrac{2}{5}\right)\)

\(=\dfrac{7}{4}.\dfrac{-12}{5}\)

\(=\dfrac{-21}{5}\)

\(#Wendy.Dang\)

Uh, chừa sau k dám học muộn nx

`a) 2,25 - x + 0,9 = 0,57`

`( 2, 25 + 0,9 ) - x = 0,57`

`3,15 - x = 0,57`

`x = 3,15 - 0,57`

`x = 2,58`

________________________________

`b) x : 0,28 xx 0,7 = 2,7`

`x : 0,28 = 2,7 : 0,7`

`x : 0,28 = 27 / 7`

`x = 27 / 7 xx 0,28`

`x = 27 / 7 xx 7 / 25`

`x = 27 / 25`

a) \(x\)là giá trị tuyệt đối của 1 số nên \(x\ge0\)

\(\Rightarrow x.\left|x-4\right|=x\)

Với x = 0 :

\(\Rightarrow\orbr{\begin{cases}x=0\\x-4=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=0\\x=4\end{cases}}\)

Với x > 0

TH1 : \(x< 4;\)ta có:

\(x.\left(4-x\right)=x\)

\(4x-x^2=x\)

\(x^2=4x-x=3x\Rightarrow x=3\)

TH2 : \(x\ge4;\)ta có:

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

\(x^2-4x=x\)

\(\Rightarrow x^2=5x\)

\(\Rightarrow x=5\)

Vậy \(x\in\left\{0;3;4;5\right\}\)

a: \(x\cdot3\cdot5=2,7\)

=>\(x\cdot15=2,7\)

=>\(x=\dfrac{2,7}{15}=0,18\)

b: \(1,2:x\cdot4=20\)

=>\(1,2:x=20:4=5\)

=>\(x=1,2:5=0,24\)