a)1/3-2/5+3×x=3/4 b)-1/10+2/5×x+7/20=1/10 Tìm x

`a) 1/3 - 2/5 + 3 xx x = 3/4`

`=> (-1)/15 + 3 xx x = 3/4`

`=> 3 xx x = 3/4 + 1/15`

`=> 3 xx x= 49/60`

`=> x = 49/60 : 3`

`=> x = 49/180`

Vậy `x = 49/180`

$\\$

`b) (-1)/10 + 2/5 xx x + 7/20 = 1/10`

`=> 2/5 xx x + 7/20 = 1/10 + 1/10`

`=> 2/5 xx x + 7/10 = 1/5`

`=> 2/5 xx = 1/5 - 7/20`

`=> 2/5 xx x = (-3)/20`

`=> x = (-3)/20 : 2/5`

`=> x = (-3)/8`

Vậy `x = (-3)/8``