\(\Leftrightarrow\left(x^2-16-x+4\right)\left(x^2-16+x-4\right)=0\)
\(\Leftrightarrow\left(x^2-x-12\right)\left(x^2+x-20\right)=0\)
\(\Leftrightarrow\left(x\left(x+3\right)-4\left(x+3\right)\right)\left(x\left(x-4\right)+5\left(x-4\right)\right)=0\)
\(\Leftrightarrow\left(x-4\right)^2\left(x+3\right)\left(x+5\right)=0\Rightarrow\left[{}\begin{matrix}x=4\\x=-3\\x=-5\end{matrix}\right.\)
https://i.imgur.com/xsYAPve.jpg
