令t=1+1/x则1/x=t-1 x=1/(t-1)f(1+1/x)=1/x+x²+1/x²=t-1+1/(t-1)²+(t-1)²=t²-t+1/(t-1)²t和x同样在定义域上取值,将t换成xf(x)=x²-x+1/(x-1)²