Step 1 :
To factor $ x^{3}-2x^{2}-25x+50 $ we can use factoring by grouping:
Group $ \color{blue}{ x^{3} }$ with $ \color{blue}{ -2x^{2} }$ and $ \color{red}{ -25x }$ with $ \color{red}{ 50 }$ then factor each group.
$$ \begin{aligned} x^{3}-2x^{2}-25x+50 = ( \color{blue}{ x^{3}-2x^{2} } ) + ( \color{red}{ -25x+50 }) &= \\ &= \color{blue}{ x^{2}( x-2 )} + \color{red}{ -25( x-2 ) } = \\ &= (x^{2}-25)(x-2) \end{aligned} $$Step 2 :
Rewrite $ x^{2}-25 $ as:
$$ x^{2}-25 = (x)^2 - (5)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = x $ and $ II = 5 $ , we have:
$$ x^{2}-25 = (x)^2 - (5)^2 = ( x-5 ) ( x+5 ) $$