a. x(x+7)=0
⇔\(\left[ \begin{array}{l}x=0\\x+7=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0\\x=-7\end{array} \right.\)
b. (x+12)(x-3)=0
⇔\(\left[ \begin{array}{l}x+12=0\\x-3=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=-12\\x=3\end{array} \right.\)
c.(-x+5)(3-x)=0
⇔\(\left[ \begin{array}{l}-x+5=0\\3-x=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=5\\x=3\end{array} \right.\)
d.x(2+x)(7-x)=0
⇔\(\left[ \begin{array}{l}x=0\\x=-2 và x=7 \end{array} \right.\)
16.a. 8:x,⇒x=1,2,4,8
b.12:x, x<0⇒x=-1;-2;-3;-4;-6;-12
mấy câu dưới a ko hiểu xin lỗi