bài 1: tìm x, biết: a) 3(5x -1) - x( x - 2) + x2 - 13x = 7 b) 4x2 - 2x + 3 - 4x(x - 5) = 7x-3 giúp mk vs

`a) 3(5x -1) - x( x - 2) + x^2 - 13x = 7`

`⇔15x-3-x^2+2x+x^2-13x=7`

`⇔(-x^2+x^2)+(15x+2x-13x)=7+3`

`⇔4x=10`

`⇔x=10:4`

`⇔x=5/2`

Vậy `x=5/2.`

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

`⇔4x^2-2x+3-4x^2+20x -7x +3=0`

`⇔(4x^2-4x^2)-(2x+7x-20x)=0-3-3`

`⇔-(-11x)=-6`

`⇔-11x=6`

`⇔x=6:(-11)`

`⇔x=-6/11.`

Vậy `x=-6/11.`