ĐKXĐ: (x + 1)(2x - 6) \(\ne\)0 <=> \(\left\{{}\begin{matrix}x+1\ne0\\2x-6\ne0\end{matrix}\right.\) <=> \(\left\{{}\begin{matrix}x\ne-1\\x\ne3\end{matrix}\right.\)
Ta có: A = 0
=> \(\frac{3x^2+3x}{\left(x+1\right)\left(2x-6\right)}=0\)
=> 3x2 + 3x = 0 (do (x + 1)(2x - 6) \(\ne\)0)
=> 3x(x + 1) = 0
=> \(\left\{{}\begin{matrix}3x=0\\x+1=0\end{matrix}\right.\)
=> \(\left\{{}\begin{matrix}x=0\left(Tm\right)\\x=-1\left(ktm\right)\end{matrix}\right.\)