x-1/x=1
x^2+1/x^2
=(x-1/x)^2+2
=1+2
=3

x^3-1/x^3
=(x-1/x)(x^2+1+1/x^2)
=1*(3+1)
=4

不懂可追问,有帮助请采纳,谢谢!x^3-1/x^3不等于(x-1/x)(x^2+1+1/x^2)(x-1/x)(x^2+1+1/x^2)=x^3+1/x+x-1/x-1/x^3-1/x