Đáp án+Giải thích các bước giải:

 `f)4x^{2}-2x+3-4x.(x-5)=7x-4`

`4x^{2}-2x+3-4x^{2}+20x=7x-4`

`18x+3-7x+4=0`

`11x+7=0`

`11x=-7`

`x=-7/11`

Vậy `x=-7/11`

`g)-3x.(x-5)+5.(x-1)+3x^{2}=4-x`

`-3x^{2}+15x+5x-5+3x^{2}=4-x`

`20x-5-4+x=0`

`21x-9=0`

`21x=9`

`x=9/21`

`x=3/7`

Vậy `x=3/7`

`h)7x.(x-2)-5.(x-1)=21x^{2}-14x^{2}+3`

`7x^{2}-14x-5x+5=7x^{2}+3`

`7x^{2}-19x+5-7x^{2}-3=0`

`-19x+2=0`

`-19x=-2`

`x=2/19`

Vậy `x=2/19`

`i)3.(5x-1)-x.(x-2)+x^{2}-13x=7`

`15x-3-x^{2}+2x+x^{2}-13x=7`

`4x=7+3`

`4x=10`

`x=10/4`

`x=5/2`

Vậy `x=5/2`

`k)1/5x.(10x-15)-2x.(x-5)=12`

`2x^{2}-3x-2x^{2}+10x=12`

`7x=12`

`x=12/7`

Vậy `x=12/7`