y=ln(x+√x²+1)即e^y=x+√x²+1所以e^(-y)=1/(x+√x²+1)=√x²+1 -x那么e^y -e^(-y)=2x所以x=[e^y -e^(-y)] /2于是反函数为：y= [e^x -e^(-x)] /2
