f(x)定义域为(-无穷,0),(0,+无穷)
-f(x)= -(x+1/x)= -x+1/(-x)= f(-x)
是奇函数
求导f’(x)=1- 1/x²=0时,x=±1
f(x)在(-1,0),(0,1)递减,(-无穷,-1),(1,无穷)递增