(3a³/a+b)³·(a²-b²)÷（b-a/b+a)²计算= 27a^9/(a+b)³ * (a-b)(a+b) × (a+b)²/(a-b)²=27a^9/(a+b)² * (a+b)² /(a-b)=27a^9 /(a-b)