先进行因式分解,得：x³+y³ =(x+y)(x²-xy+y²) =(x+y)[(x+y)²-3xy]=2···········① 由于(x-y)²≥0,展开即得：2xy≤x²+y² 4xy≤x²+2xy+y² 4xy≤(x+y)
...