\(a\times5:6=25\)

\(a\times5=25\times6\)

\(a\times5=150\)

\(a=150:5\)

\(a=30\)

\(a\times5:6=25\\ a\times\dfrac{5}{6}=25\\ a=25:\dfrac{5}{6}\\ a=25\times\dfrac{6}{5}\\ a=30\)

a x 5 : 6 = 25

a x 5      = 25 x 6

a x 5      = 150

a            =150 : 5

a            = 30

x/5 + x2 + x/5:1/2=13

x/5 + x.2 + x/5 x 2 = 13

x/5.(1 + 2 ) + 2x = 13

x/5 .3 +2x = 13

3x/5 + 2x = 13

3x + 10x = 65

13x = 65

x = 65 : 13

x = 5

1,-12 + x = 5x - 20

-12 + 20 = 5x - x

8 = 4x

x = 2

2, 7x - 4 = 20 + 3x

7x - 3x = 20 + 4

4x = 24

x  = 6

3 , 5x - 7 = -21 - 2x

5x + 2x  = -21 + 7

7x = -14

x = -14 : 7 = -2

4 , x + 15  = 20 - 4x

x + 4x = 20 - 15

5x = 5

x = 5 : 5 = 1

5, 17 - x = 7 - 6x

-x + 6x = 7 - 17

5x = -10

x = -10 : 5 = -2

Số số hạng là :

\(\left(x-2\right):2+1=x:2-1+1=x:2\) (số hạng)

Tổng trên là :

\(\left(x+2\right).x:2:2=42\)

\(\left(x+2\right).x=42.2.2\)

\(\left(x+2\right).x=168\)

\(\left(x+2\right).x=14.12\)

                          Vậy x = 14

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

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

\(x=\frac{9}{20}\)

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

\(\left|x+\frac{3}{4}\right|=0+\frac{1}{2}\)

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

\(\Rightarrow\hept{\begin{cases}x+\frac{3}{4}=\frac{1}{2}\\x+\frac{3}{4}=-\frac{1}{2}\end{cases}\Rightarrow\hept{\begin{cases}x=\frac{-1}{4}\\x=\frac{-5}{4}\end{cases}}}\)

Vậy x=-1/4 hoặc x=-5/4

c) \(\left(x+\frac{1}{3}\right)^3=\frac{-1}{8}\)

\(\Leftrightarrow x+\frac{1}{3}=\frac{-1}{8}=\frac{\left(-1\right)^3}{2^3}=\frac{-1}{2}\)

\(x=\frac{-1}{2}-\frac{1}{3}\)

\(x=\frac{-5}{6}\)

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

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

\(\frac{2}{3}x=\frac{3}{10}\)

\(x=\frac{3}{10}:\frac{2}{3}\)

\(x=\frac{9}{20}\)

b) l x + 3/4 l - 1/2 = 0

    l x + 3/4 l = 1/2

TH1 : \(x+\frac{3}{4}\le0\)                           TH2: \(x+\frac{3}{4}\ge0\)

=> \(x+\frac{3}{4}=-\frac{1}{2}\)                             =>   \(x+\frac{3}{4}=\frac{1}{2}\)

   \(x=-\frac{1}{2}-\frac{3}{4}\)                                            \(x=\frac{1}{2}-\frac{3}{4}\)

       \(x=-\frac{5}{4}\)                                                  \(x=-\frac{1}{4}\)

c) ( x + 1/3 )³ = ( -1/8 )

( x + 1/3 ) ³ = ( -1/3 )³

=> x + 1/3 = -1/3

x = -1/3 - 1/3

x = -2/3

3/5 : x = 3

        x = 3/5 : 3

        x = 3/5 x 1/3

        x = 1/5

3/5 : x = 3

x = 3/5 : 3/1

x = 3/5 x 1/3

x= 3/15

x = 1/5

\(\frac{3}{5}:x=3\)

\(x=\frac{3}{5}:3\)

\(x=\frac{3}{5}.\frac{1}{3}\)

\(x=\frac{1}{5}\)

P/s: dấu (.) là nhân