[tex]\bf 4(x+5)^3(x-1)^2-(x+5)^4\cdot 2(x-1)
\\\\\\
4(x+5)^3(x-1)^2-2(x-1)(x+5)^4
\\\\\\ \underline{2}\cdot 2\underline{(x+5)^3}(x-1)\underline{(x-1)}~-~\underline{2}\underline{(x-1)}(x+5)\underline{(x+5)^3}\leftarrow
\begin{array}{llll}
notice~the\\
common\\ \underline{factors}
\end{array}
\\\\\\
2(x+5)^3(x-1)~[~2(x-1)-(x+5)~]
\\\\\\
2(x+5)^3(x-1)~[2x-2-x-5]\implies 2(x+5)^3(x-1)(x-7)[/tex]
