x³+x-x²-1
=x^2(x-1)+x-1
=(x^2-1)(x-1)
=(x+1)(x-1)^2
x<-1时x³+x-x²-1<0
x³+xx=1,或x=-1时x³+x-x²-1=0
x³+x=x²+1
-11时x³+x-x²-1>0
x³+x>x²+1