Lời giải:
$a.(x+2).(x-4)>0$
<=>\(\left[ \begin{array}{l}x+2>0\\x-4>0\end{array} \right.\)
<=>\(\left[ \begin{array}{l}x>-2\\x>4\end{array} \right.\)
$b.(3-x).(x-1)\leq0$
<=>\(\left[ \begin{array}{l}3-x\leq0\\x-1\leq0\end{array} \right.\)
<=>\(\left[ \begin{array}{l}x\geq3\\x\leq1\end{array} \right.\)
$c.(x^2+5).(2-x)\geq0$
<=>\(\left[ \begin{array}{l}x^2+5\geq0\\2-x\geq0\end{array} \right.\)
<=>\(\left[ \begin{array}{l}x^2\geq-5(loại)\\x\leq2\end{array} \right.\)
$d.(1+x).(x-1)^2.(x-3)<0$
<=>$\left[\begin{array}{l}
1+x<0 \\
(x-1)^2<0 \\
x-3<0
\end{array}\right.$
<=>$\left[\begin{array}{l}
x<-1 \\
x<1\\
x<3
\end{array}\right.$
