a. x.(x - 2) + x - 2 = 0
\(\Leftrightarrow\)x(x-2)+(x-2)=0
\(^{_{ }\Leftrightarrow}\)(x-2)(x+1)=0
\(\left[{}\begin{matrix}x-2=0\\x+1=0\end{matrix}\right.\Leftrightarrow\)\(\left[{}\begin{matrix}x=2\\x=-1\end{matrix}\right.\)
Vậy x\(\in\)\(\left\{2;-1\right\}\)
b. 5x(x-3)-(x+3)
\(^{_{ }\Leftrightarrow}\)5x(x-3) + (x-3) = 0
\(^{_{ }\Leftrightarrow}\)(x-3)(5x+1) = 0
\(\Rightarrow\)\(\left\{{}\begin{matrix}x-3=0\\5x+1=0\end{matrix}\right.\)\(\Rightarrow\)\(\left\{{}\begin{matrix}x=3\\x=\dfrac{-1}{5}\end{matrix}\right.\)
Vậy...