(3𝑥 − (𝑦 + 1)/3 ) [9x² − 𝑥(𝑦 + 1) + (𝑦 + 1)² /9 ][9x²+ 𝑥(𝑦 + 1) + (𝑦 + 1)²/ 9 ] (3𝑥 + (𝑦 + 1)/3
note the pattern where $a = 3x$ and $b = \dfrac{y+1}{3}$(3𝑥 − (𝑦 + 1)/3 ) [9x² − 𝑥(𝑦 + 1) + (𝑦 + 1)² /9 ][9x²+ 𝑥(𝑦 + 1) + (𝑦 + 1)²/ 9 ] (3𝑥 + (𝑦 + 1)/3
$(a-b)(a^2-ab+b^2)(a^2+ab+b^2)(a+b)$
$\left[(a-b)(a^2+ab+b^2)\right] \cdot \left[(a^2-ab+b^2)(a+b)\right]$
$(a^3-b^3)(a^3+b^3) = a^6 - b^6$