>>40
y=e^x-e^(-x)/e^x+e^(-x)とおくと
e^x=(1+y)/(1-y)より
x=log(1+y)/(1-y)=log(1+y)-log(1-y)
よってdx/dy=1/(1+y) - 1/(1-y)=2/(1+y)(1-y)