b) Tui làm theo kết quả của bà đó nha!
Sai thì đừng trách đó!
\(\left|A\right|=3\) \(\Leftrightarrow\left|\frac{x+1}{x-3}\right|=3\)
\(\Leftrightarrow\left[{}\begin{matrix}\frac{x+1}{x-3}=3\\\frac{x+1}{x-3}=-3\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x+1=3\left(x-3\right)\\x+1=-3\left(x-3\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x+1=3x-9\\x+1=-3x+9\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}1+9=3x-x\\x+3x=9-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}2x=10\\4x=8\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=5\\x=2\end{matrix}\right.\left(TM\right)\)
