\(\color{blue}(a + b)^3 = a^3 + 3a^2b + 3ab^2 + b^3\)
\(\text{Misal:, }\)
\(a = x\)
\(b = 3y\)
\begin{equation*}
\begin{split}
(x + 3y)^3& = x^3 + 3(x)^2(3y) + 3x(3y)^2 + (3y)^3\\\\
(x + 3y)^3& = x^3 + 9x^2y + 27xy^2 + 27y^3
\end{split}
\end{equation*}