TeX source:

\begin{aligned}&f(x)=x^{4}-12 x^{3}+30 x^{2}+5 x-7 . f^{\prime}(x)=4 x^{3}-36 x^{2}+60 x+5 \\&f^{\prime \prime}(x)=12 x^{2}-72 x+60=12\left(x^{2}-6 x+5\right)=12(x-1)(x-5)\end{aligned}