Đáp án:
$c)x>0\\ d)x\ge 3\\ e) -2< x \le 1.$
Giải thích các bước giải:
$c)\text{ĐKXĐ}: x \ne 0\\ \dfrac{4x}{5|x|}>0 \Leftrightarrow 4x>0(\text{Do } 5|x|>0 \ \forall \ x \ne 0)\\ \Leftrightarrow x>0\\ d)\dfrac{x-3}{x^2+4} \ge 0\\ \Leftrightarrow x-3\ge 0(\text{Do } x^2+4 \ \forall \ x \ne 0)\\ \Leftrightarrow x\ge 3\\ e)\text{ĐKXĐ}: x \ne -2\\ \dfrac{x-1}{x+2} \le 0\\ \Leftrightarrow \left[\begin{array}{l} \left\{\begin{array}{l} x-1 \ge 0 \\ x+2 <0\end{array} \right.\\ \left\{\begin{array}{l} x-1 \le 0 \\ x+2 >0\end{array} \right.\end{array} \right.\\ \Leftrightarrow \left[\begin{array}{l} \left\{\begin{array}{l} x \ge 1 \\ x<-2\end{array} \right.(\text{Vô lí})\\ \left\{\begin{array}{l} x \le 1\\ x>-2\end{array} \right.\end{array} \right.\\ \Leftrightarrow -2< x \le 1.$
