TH1:

$\left\{ \begin{align}& x+\frac{3}{4}>0 \\ & x-3>0 \\ \end{align} \right.$

$\Rightarrow $ $\left\{ \begin{align} & x>-\frac{3}{4} \\ & x>3 \\ \end{align}\right.$

$\Rightarrow $x>3

TH2:

$\left\{ \begin{align}& x+\frac{3}{4}<0 \\ & x-3<0 \\ \end{align} \right.$

$\Rightarrow $ $\left\{ \begin{align} & x<-\frac{3}{4} \\ & x<3 \\ \end{align}\right.$

$\Rightarrow $x<$-\frac{3}{4}$

Vậy x>3 hoặc x<$-\frac{3}{4}$