Câu 7:
$(-14)x+4(7+x)=-72$
⇔ $-14x+28+4x=-72$
⇔ $-10x=-72-28$
⇔ $-10x=-100$
⇔ $x=10$
Vậy S={10}
Câu 8:
$ |x-2|.(-6)=-48$
⇔ $ |x-2|=8$
⇔ \(\left[ \begin{array}{l}x-2=8\\x-2=-8\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=10\\x=-6\end{array} \right.\)
Vậy S={-6;10}
Câu 9:
$(12-x)(x+4)=0$
⇔ \(\left[ \begin{array}{l}12-x=0\\x+4=0\end{array} \right.\)
⇔ \(\left[ \begin{array}{l}x=12\\x=-4\end{array} \right.\)
Vậy S= {-4; 12}
Câu 10:
$12:x^2-18=-15$
⇔ $12:x^2=-15+18$
⇔ $12:x^2=3$
⇔ $x^2=12:3$
⇔ $x^2=4$
⇔ \(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
Vậy S= {-2; 2}
