$(x - 4)^{2}$ - 36 = 0
<=> $(x - 4)^{2}$ - $6^{2}$ = 0
<=> (x - 4 - 6)(x - 4 + 6) = 0
<=> (x - 10)(x + 2) = 0
<=> $\left \{ {{x - 10 = 0} \atop {x + 2 = 0}} \right.$
<=>\(\left[ \begin{array}{l}x=10\\x=-2\end{array} \right.\)
Vậy x = { -2 ; 10 }
b, $(x + 8)^{2}$ = 121
<=> $\left \{ {{x + 8=11} \atop {x + 8= -11}} \right.$
<=> \(\left[ \begin{array}{l}x=3\\x=-19\end{array} \right.\)
Vậy x = { 3 ; -19}
c, $x^{2}$ + 8x + 16 = 0
<=> $x^{2}$ + 2. 4x + $4^{2}$ = 0
<=> $(x + 4)^{2}$ = 0 => x = -4
Vậy x = -4
d, $4x^{2}$ - 12x = -9
<=> $4x^{2}$ - 12x + 9 = 0
<=> $(2x)^{2}$ - 2 . 2x . 3 + $3^{2}$ = 0
<=> $(2x - 3)^{2}$ = 0
=> x = $\frac{3}{2}$
