`a, 4x(x-5)-(x-1)(4x-3)=23`
$\Rightarrow$ ` 4x^2-20x-4x^2+7x-3=23`
$\Rightarrow$ `-13x-3=23`
$\Rightarrow$ `-13x=23+3`
$\Rightarrow$ `-13x=26`
$\Rightarrow$ `x=-2`
$\text{Vậy x = 8}$
`b,(x-5)(x-4)-(x+1)(4x-3)=23`
$\Rightarrow$ `x(x-4)-5(x-4)-x(x-2)-(x-2)=7`
$\Rightarrow$ `x^2-4x-5x+20-x^2+2x-x+2=7`
$\Rightarrow$ `-8x+22=7`
$\Rightarrow$ `-8x=-15`
$\Rightarrow$ `x=15/8`
$\text{Vậy x = }$ `15/8`