Giải thích các bước giải:

a.$3x(25x+15)-7(5x+3)=0$

$\to 75x^2+45x-35x-21=0$

$\to 75x^2+10x-21=0$

$\to (15x-7)(5x+3)=0$

$\to x\in\{\dfrac7{15}, -\dfrac35\}$

b.$(x^2+1)(4x-3)=(x^2+1)(x-5)$

$\to 4x-3=x-5 $ vì $x^2+1>0$

$\to 3x=-2$

$\to x=-\dfrac23$

c.$(4x^2-9)-(x+2)(3-2x)=0$

$\to 4x^2-9+2x^2+x-6=0$

$\to 6x^2+x-15=0$

$\to (2x-3)(3x+5)=0$

$\to x\in\{\dfrac32, -\dfrac53\}$

d.$(x+2)(3-4x)=x^2+4x+4$

$\to (x+2)(3-4x)=(x+2)^2$

$\to (x+2)(3-4x)-(x+2)^2=0$

$\to (x+2)(3-4x-x-2)=0$
$\to (x+2)(1-5x)=0$

$\to x\in\{-2, \dfrac15\}$