(x/3+2Y)³
aplicam formula (a+b)³ = a³+3a²b+3ab²+b³ ⇒
x³/3³+3*x²/3²+3*x/3*2²y²+2³y³ = aducem la acelasi numitor comun 3³ ⇒
x³/3³+3²*2*x²y/3³+3³*2²*xy²/3³+3³*2³*y³/3³=
x²/3³(x+3²*2y)+3³*y²/3³(2²x+2³y)
x²/3³(x+3²*2y)+3³*2²*y²/3³(x+2y)
x²/27(x+18y)+4y²/27(x+2y)
