đúng vote cho 5s luôn

`a)` `0,25x+7/12=13/18-1/9`

`0,25x+7/12=11/18`

`0,25x=11/18-7/12`

`0,25x=1/36`

`x=1/36:0,25`

`x=1/9`

Vậy `x=1/9`

``

`b)` `(-7)/(1+2x)=5/(2-3x)`

`-7(2-3x)=(1+2x). 5`

`-14+21x=5+10x`

`21x-10x=5+14`

`11x=19`

`x=19/11`

Vậy `x=19/11`

`c)` `8. 3^x-3^(x+1)=2^3. 3^2+63`

`8. 3^x-3^x. 3^1=8. 9+63`

`3^x(8-3^1)=72+63`

`3^x.(8-3)=135`

`3^x. 5=135`

`3^x=135:5`

`3^x=27`

`3^x=3^3`

`x=3`

Vậy `x=3`