a) Ta có:
\(x\left(x-2\right)>0\)
\(\Rightarrow\)\(\hept{\begin{cases}x< 0\\x-2< 0\end{cases}}\)hoặc \(\hept{\begin{cases}x>0\\x-2>0\end{cases}}\)
\(\Rightarrow\hept{\begin{cases}x< 0\\x< 2\end{cases}}\)hoặc \(\hept{\begin{cases}x>0\\x>2\end{cases}}\)
\(\Rightarrow x< 0\)hoặc \(x>2\)thì x(x-2) >0.
b) \(x^2-5x=0\Rightarrow x\left(x-5\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x=0\\x-5=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=0\\x=5\end{cases}}\)