用配凑法比较简单.
f(x-1/x)=x²+1/x²+1=x²-2+1/x²+3=(x-1/x)²+3
x和x-1/x同样在定义域上取值,且1/x有意义,x≠0.将x-1/x换成x
f(x)=x²+3 (x≠0)