2f(x)+f(1/x)=3x.(1)
2f(1/x)+f(x)=3/x.(2)
(1)*2-(2)；
4f(x)-f(x)=6x-3/x
3f(x)=6x-3/x
f(x)=2x-1/x
f(1/x)=2/x-x
f(x)+f(1/x)=2x-1/x+2/x-x
=x+1/x
设y=f(x)+f(1/x)
=x+1/x
xy=x^2+1
x^2-yx+1=0
(x-y/2)^2=-1+y^2/4
x-y/2=±√(y^2-4)/2
x=[y±√(y^2-4)]/2
y^2-4>=0
y^2>=4
y=2
f(x)+f(1/x)的值域：(-∞,-2]U[2,+∞)