f(x-1/x)=x^3-1/x^3
=(x-1/x)(x^2+1/x^2+1)
=(x-1/x)[(x^2+1/x^2-2)+3]
=(x-1/x)[(x-1/x)^2+3]
则设x-1/x=T
则f(T)=T*(T^2+3)
=T^3+3T
则f(x)=x^3+3x
f(x-1/x)=x^3-1/x^3
=(x-1/x)(x^2+1/x^2+1)
=(x-1/x)[(x^2+1/x^2-2)+3]
=(x-1/x)[(x-1/x)^2+3]
则设x-1/x=T
则f(T)=T*(T^2+3)
=T^3+3T
则f(x)=x^3+3x