\(\Leftrightarrow\left(x-4\right)\left(x+4\right)+\left(x-4\right)\left(x^2+7x+1\right)=0\)
\(\Leftrightarrow\left(x-4\right)\left(x^2+8x+5\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\x^2+8x+5=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\pm\sqrt{11}\end{matrix}\right.\)