x2 - 10x + 2x - 20 = 0
⇔ x(x - 10) + 2( x - 10) = 0
⇔ ( x + 2) ( x - 10) = 0
=> x + 2 = 0 hoặc x - 10 = 0
+ x + 2 = 0 ⇔ x = -2
+ x - 10 = 0 ⇔ x = 10
Vậy...
x2 - 10x + 2x - 20 = 0
\(\Leftrightarrow\)(x2 - 10x )+ (2x - 20 )= 0
\(\Leftrightarrow\)x(x - 10 )+ 2(x - 10 )= 0
\(\Leftrightarrow\)(x - 10 )(x+2)= 0
\(\Leftrightarrow\)\(\left[{}\begin{matrix}x-10=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-2\end{matrix}\right.\)
Vậy x= 10 hoặc x= -2
x2 - 10x + 2x - 20 = 0
⇔(x2 - 10x )+ (2x - 20 )= 0
⇔x(x - 10 )+ 2(x - 10 )= 0
⇔(x - 10 )(x+2)= 0
\(\Leftrightarrow\left[{}\begin{matrix}x-10=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-2\end{matrix}\right.\)
kết luận : vậy x = 10 hoặc x = -2