比较大小,一般采用作差.
a－b=(x^3＋y^3)－(x²y＋xy²)=(x^3－x²y)＋(y^3－xy²)=x²(x－y)＋y²(y－x)=(x－y)(x²－y²)=(x－y)²(x＋y)≥0,所以a≥b.