Giải thích các bước giải:
$3x^2-45x^2$
$=3x^2.(1-15)$
$=3x^2.(-14)$
$x^2-5x+xy-5y$
$=(x^2+xy)-(5x+5y)$
$=x.(x+y)-5.(x+y)$
$=(x+y).(x-5)$
$(x-1)(x+2)-x.(x-2)=-5$
<=> $x^2+2x-x-2-x^2+2x+5=0$
<=> $3x+3=0$
<=> $3x=-3$
<=> $x=-1$
$3x(x-5)-10+2x=0$
<=> $3x(x-5)-(10-2x)=0$
<=> $3x(x-5)-2.(x-5)=0$
<=> $(x-5).(3x-2)=0$
<=> \(\left[ \begin{array}{l}x-5=0\\3x-2=0\end{array} \right.\)
<=> \(\left[ \begin{array}{l}x=5\\x=\frac{2}{3}\end{array} \right.\)