a/
$3x+9=12$
$⇔3(x+3)=12$
$⇔x+3=4$
$⇔x=1$
vậy$ x=1$
b/
$2x-43=15$
$⇔2x=15+43$
$⇔2x=58$
$⇔x=29$
vậy x=29
c/
$128-3(x+4)=23$
$⇔116-3x=23$
$⇔3x=116-23$
$⇔3x=93$
$⇔x=31$
vậy $x=31$
d/
(3x-$2^{4}$ ).7³=2.$7^{4}$
$⇔3x-2^{4}=2.7^{4}:7^{3}$
$⇔3x-16=2.7$
$⇔3x-16=14$
$⇔3x=30$
$⇔x=10$
vậy x=10
f/
$(x-6)²=9$
⇔\(\left[ \begin{array}{l}x-6=3\\x-6=-3\end{array} \right.\) ⇔\(\left[ \begin{array}{l}x=9\\x=3\end{array} \right.\)
vậy x=9 hoạc x=3
