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.
\(4x\left(x-2\right)+8x-16=0\)
\(\Leftrightarrow4x\left(x-2\right)+8\left(x-2\right)=0\)
\(\Leftrightarrow\left(4x+8\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}4x+8=0\\x-2=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=-2\\x=2\end{matrix}\right.\)
