a) x2 + 4x -5 = 0
\(\Leftrightarrow\) x2 -x + 5x - 5 = 0
\(\Leftrightarrow\)x ( x -1 ) + 5 ( x -1 ) =0
\(\Leftrightarrow\) ( x+5)(x-1) = 0
\(\Rightarrow\)\(\left\{{}\begin{matrix}x+5=0\\x-1=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=-5\\x=1\end{matrix}\right.\)