<=>x^2-4x-5x+20=0
<=>x(x-4)-5(x-4)=0
<=>(x-5)(x-4)=0
=>x=5; x=4
\(x^2-9x+20=0\)
\(\Leftrightarrow x^2-4x-5x+20=0\)
\(\Leftrightarrow\left(x^2-4x\right)-\left(5x-20\right)=0\)
\(\Leftrightarrow x\left(x-4\right)-5\left(x-4\right)=0\)
\(\Leftrightarrow\left(x-4\right)\left(x-5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\x-5=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=5\end{matrix}\right.\)
Vậy \(x=4\) hoặc \(x=5\)
x2-9x+20=0
<=>x2 - 4x-5x +20 =0
<=>x(x-4) -5(x-4)=0
<=>(x-5)(x-4) =0
<=> x-5=0 hoặc x-4=0
<=> x=5 hoặc x=4
Vậy x=5 hoặc x=4
