順便求解(a+b+c)^3=? a^3+b^3+c^3=?

⑵
由題組⑴ , (∛2 + 1)³ (∛2 - 1) = (∛2 + 1)(∛2 - 1) (∛2 + 1)² = (∛4 - 1) (∛4 + 2∛2 + 1)
= ∛16 + 2∛8 + ∛4 - (∛4 + 2∛2 + 1) = 2∛2 + 4 + ∛4 - (∛4 + 2∛2 + 1) = 4 - 1 = 3

故得 ∛2 - 1 = 3 / (∛2 + 1)³
⇒ ∛(∛2 - 1) = ∛ ( 3 / (∛2 + 1)³ ) = ∛3 / (∛2 + 1) = ∛3 / ( (2 + 1) / (∛4 - ∛2 + 1) ) = (∛4 - ∛2 + 1) / ∛9
= ∛(4/9) - ∛(2/9) + ∛(1/9)

∴ a + b + c = 4/9 - 2/9 + 1/9 = 1/3