p³=a-3a^(2/3)b^(1/3)+3a^(1/3)b^(2/3)-b
=a-b-3a^(1/3)b^(1/3)[a^(1/3)-b^(1/3)]
q³=a-b
a>0,b>0
a≥b
所以3a^(1/3)>0
b^(1/3)>0
a^(1/3)-b^(1/3)≥0
所以-3a^(1/3)b^(1/3)[a^(1/3)-b^(1/3)]≤0
所以p³-q³≤0
p≤q