2.\(12x^3+8x=4x\left(3x^2+2\right)\)\(x^2-49=x^2-7^2=\left(x-7\right)\left(x+7\right)\)\(2xy+6x+y^2-9=2x\left(y+3\right)+\left(y-3\right)\left(y+3\right)=\left(y+3\right)\left(2x+y-3\right)\)3.a.\(\left(x-1\right)\left(5x+3\right)+4-5x^2=6\)\(\Leftrightarrow5x^2+3x-5x-3+4-5x^2=6\)\(\Leftrightarrow-2x=5\)\(\Leftrightarrow x=-\dfrac{5}{2}\)b.\(4x\left(x-2\right)+8x-16=0\)\(\Leftrightarrow4x\left(x-2\right)+8\left(x-2\right)=0\)\(\Leftrightarrow\left(4x+8\right)\left(x-2\right)=0\)\(\Leftrightarrow\left[{}\begin{matrix}4x+8=0\\x-2=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=2\end{matrix}\right.\)Câu trả lời: 2.\(12x^3+8x=4x\left(3x^2+2\right)\)\(x^2-49=x^2-7^2=\left(x-7\right)\left(x+7\right)\)\(2xy+6x+y^2-9=2x\left(y+3\right)+\left(y-3\right)\left(y+3\right)=\left(y+3\right)\left(2x+y-3\right)\)3.a.\(\left(x-1\right)\left(5x+3\right)+4-5x^2=6\)\(\Leftrightarrow5x^2+3x-5x-3+4-5x^2=6\)\(\Leftrightarrow-2x=5\)\(\Leftrightarrow x=-\dfrac{5}{2}\)b.\(4x\left(x-2\right)+8x-16=0\)\(\Leftrightarrow4x\left(x-2\right)+8\left(x-2\right)=0\)\(\Leftrightarrow\left(4x+8\right)\left(x-2\right)=0\)\(\Leftrightarrow\left[{}\begin{matrix}4x+8=0\\x-2=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=2\end{matrix}\right.\)