x^2(x-y)-y^2(x-y)
=(x-y)(x^2-y^2)
=(x-y)(x-y)(x+y)
=(x-y)^2(x+y)
x,y均为正数,则x+y>0
x,y互不相等,则(x-y)^2>0
因此(x-y)^2(x+y)>0
x^2(x-y)-y^2(x-y)>0
x^2(x-y)>y^2(x-y)