\(x\left(x-5\right)-4x+20\) \(=0\)\(\Rightarrow x\left(x-5\right)-4\left(x-5\right)=0\)\(\Rightarrow\left(x-4\right)\left(x-5\right)=0\)\(\Rightarrow\hept{\begin{cases}x-4=0\\x-5=0\end{cases}}\Rightarrow\hept{\begin{cases}x=4\\x=5\end{cases}}\)Câu trả lời: \(x\left(x-5\right)-4x+20\) \(=0\)\(\Rightarrow x\left(x-5\right)-4\left(x-5\right)=0\)\(\Rightarrow\left(x-4\right)\left(x-5\right)=0\)\(\Rightarrow\hept{\begin{cases}x-4=0\\x-5=0\end{cases}}\Rightarrow\hept{\begin{cases}x=4\\x=5\end{cases}}\)