a) (X+1)×(3-X)=0
(=)\(\left[ \begin{array}{l}x+1=0\\3-x=0\end{array} \right.\)(=)\(\left[ \begin{array}{l}x=-1\\x=3\end{array} \right.\)
b) (X-2)×(2×X-1)=0
(=)\(\left[ \begin{array}{l}x-2=0\\2x-1=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=2\\2x=1\end{array} \right.\) (=)\(\left[ \begin{array}{l}x=2\\x=\frac{1}{2}\end{array} \right.\)
c)(3×X+9)×(1-3×X)=0
(=)\(\left[ \begin{array}{l}3x+9=0\\1-3x=0\end{array} \right.\) (=)\(\left[ \begin{array}{l}3x=-9\\-3x=-1\end{array} \right.\) (=) \(\left[ \begin{array}{l}x=-3\\x=\frac{1}{3} \end{array} \right.\)
d)(X²+1)×(81-X²)=0
(=)\(\left[ \begin{array}{l}x^{2}+1=0 \\81-x^{2}=0 \end{array} \right.\) (=)\(\left[ \begin{array}{l}x^{2}=-1=)vô lý\\x^{2}=81\end{array} \right.\) =)x=±9
