y=ln[x+(2^2+1)^(1/2)]=ln[x+5^(1/2)]
x+5^(1/2)>0,x>-5^(1/2),
x+5^(1/2)=e^y
x=e^y-5^(1/2)
反函数：y=e^x-5^(1/2),x属于R