Step 1 :
To factor $ 2x^{3}-3x^{2}-18x+27 $ we can use factoring by grouping:
Group $ \color{blue}{ 2x^{3} }$ with $ \color{blue}{ -3x^{2} }$ and $ \color{red}{ -18x }$ with $ \color{red}{ 27 }$ then factor each group.
$$ \begin{aligned} 2x^{3}-3x^{2}-18x+27 = ( \color{blue}{ 2x^{3}-3x^{2} } ) + ( \color{red}{ -18x+27 }) &= \\ &= \color{blue}{ x^{2}( 2x-3 )} + \color{red}{ -9( 2x-3 ) } = \\ &= (x^{2}-9)(2x-3) \end{aligned} $$Step 2 :
Rewrite $ x^{2}-9 $ as:
$$ x^{2}-9 = (x)^2 - (3)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = x $ and $ II = 3 $ , we have:
$$ x^{2}-9 = (x)^2 - (3)^2 = ( x-3 ) ( x+3 ) $$