Đáp án + Giải thích các bước giải:
`a)` `2/3x+5/7=3/10`
`=>2/3x=3/10-5/7`
`=>2/3x=21/70-50/70`
`=>2/3x=-29/70`
`=>x=(-29/70):2/3`
`=>x=(-29/70)*3/2`
`=>x=-87/140`
Vậy `x = -87/140`
`b)` `3/4x-1/2=3/7`
`=>3/4x=3/7+1/2`
`=>3/4x=6/14+7/14`
`=>3/4x=13/14`
`=>x=13/14:3/4`
`=>x=13/14*4/3`
`=>x=26/21`
Vậy `x = 26/21`
`c)` `(-21)/13x+1/3=(-2)/3`
`=>(-21)/13x=(-2)/3-1/3`
`=>(-21)/13x=-1`
`=>x=(-1):(-21)/13`
`=>x=(-1)*(-13)/21`
`=>x=13/21`
Vậy `x = 13/21`.