\(D=27x^3-\dfrac{1}{8}y^3\)
\(D=\left(3x\right)^3-\left(\dfrac{1}{2}y\right)^3\)
\(D=\left(3x-\dfrac{1}{2}y\right)\left(9x^2+3x.\dfrac{1}{2}y+\dfrac{1}{4}y^2\right)\)
\(C=\left(x^2+2x+3\right)^2-9\)
\(C=\left(x^2+2x+3\right)^2-3^2\)
\(C=\left(x^2+2x+3+3\right)\left(x^2+2x+3-3\right)\)
\(C=\left(x^2+2x+6\right)\left(x^2+2x\right)\)