bài 1: tìm x, biết: a) 1/3x + 2/5 (x-1)=0 b) 4/x+2 = 5/2x + 1

 a) `1/3x + 2/5(x-1) =0`

`1/3 x + 2/5 x – 2/5 = 0`

`11/15 x = 2/5`

`x= 6/11`

b) `4/(x+2) = 5/(2x+1)`

`4(2x+1) = 5(x+2)`

`8x + 4 = 5x + 10`

`8x – 5x = 10 -4`

`3x = 6`

`x=2`