a,  x - 3 : 2 = 5 14 : 5 12

=>  x - 3 : 2 = 5 2

=>  x - 3 : 2 = 25

=> x – 3 = 25

=> x = 53

b,  30 : x - 7 = 15 19 : 15 18

=>  30 : x - 7 = 15

=> x – 7 = 2

=> x = 9

c,  x 70 = x

=>  x 70 - x = 0

=>  x ( x 69 - 1 ) = 0

=> 

d,  2 x + 1 3 = 9 . 81

=>  2 x + 1 3 = 9 3

=> 2x + 1 = 9

=> x = 4

e,  5 x + 5 x + 2 = 650

=>  5 x 1 + 5 2 = 650

=>  5 x . 26 = 650

=>  5 x = 25

=> x = 2

f,  4 x - 1 2 = 25 . 9

=> 4 x - 1 2 = 5 2 . 3 2

=>  4 x - 1 2 = 15 2

=> 4x – 1 = 15

=> x = 4

moi hok lop 6

a,\(\left(x+2\right)^2=81>0\)

\(\orbr{\begin{cases}\left(x+2\right)^2=9^2\\\left(x+2\right)^2=\left(-9\right)^2\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x+2=9\\x+2=-9\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=7\\x=-11\end{cases}}\)

a)\(\left(x+2\right)^2=81\\ =>\left(x+2\right)=9^2hay\left(x+2\right)=\left(-9\right)^2\)

x+2=9                     x+2=-9

x=9-2                      x=-9-2

x=7(TM)                  x=-11(TM)

        Vậy x=7 hay x=-9

a)

<=> 10x - 35 + 16x - 10 = 5 

<=> 10x + 16x = 5 + 35 + 10

<=> 26x = 50

<=> x = 50/26 = 25/13