bài 1.tìm x a.12x^2-4x(3x+5)=10x-17 b.-4x(x-5)+7x(x-4)-3x^2=12 c.4x^2-2x+3-4x(x+5)=7x-3

`a)` `12x^2-4x(3x+5)=10x-17`

`=12x^2-12x^2-20x=10x-17`

`<=>-20x-10x+17=0`

`<=>-30x=0-17`

`<=>-30x=-17`

`<=>x=17/30`

Vậy `x=17/30`

`b)` `-4x(x-5)+7x(x-4)-3x^2=12`

`<=>-4x^2+20x+7x^2-28x-3x^2=12`

`<=>(-4x^2+7x^2-3x^2)+(20x-28x)=12`

`<=>-8x=12`

`<=>x=12:(-8)`

`<=>x=-3/2`

Vậy `x=-3/2`

`c)` `4x^2-2x+3-4x(x+5)=7x-3`

`<=>4x^2-2x+3-4x^2-20x=7x-3`

`<=>4x^2-2x+3-4x^2-20x-7x+3=0`

`<=>(4x^2-4x^2)+(-2x-20x-7x)+(3+3)=0`

`<=>-29x+6=0`

`<=>-29x=-6`

`<=>x=6/29`

Vậy `x=6/29`