$2(x-3)(x²+1)+15x-5x²=0$
$⇔2(x-3)(x²+1)+5x(3-x)=0$
$⇔2(x-3)(x²+1)-5x(x-3)=0$
$⇔(x-3).[(2(x²+1)-5x]=0$
$⇔(x-3).(2x²-5x+2)=0$
$⇔(x-3).(2x²-4x-x+2)=0$
$⇔(x-3).[2x(x-2)-(x-2)]=0$
$⇔(x-3).(x-2)(2x-1)=0$
$⇔x-3=0$ hoặc $x-2=0$ hoặc $x-1=0$
$⇔x=3$ hoặc $x=2$ hoặc $x=1$