\(\left(6x-\dfrac{1}{3}\right)\left(36x^2+2x+\dfrac{1}{9}\right)\)
\(=\left(6x-\dfrac{1}{3}\right)\left[\left(6x\right)^2+6x.\dfrac{1}{3}+\left(\dfrac{1}{3}\right)^2\right]\)
\(=\left(6x\right)^3-\left(\dfrac{1}{3}\right)^3\)
\(=216x^3-\dfrac{1}{27}\)