x2 + 4x - 9 +4 = 0
<=> x2 + 4x - 5 = 0
<=> x2 - x + 5x - 5 = 0
<=> x(x - 1) + 5(x - 1) = 0
<=> (x - 1)(x + 5) = 0
<=> \(\left[{}\begin{matrix}x-1=0\\x+5=0\end{matrix}\right.\) <=> \(\left[{}\begin{matrix}x=1\\x=-5\end{matrix}\right.\)
Vậy x ={1; -5}