Let and you'll get a quadratic in . Solve for , substitute again and take natural logs.
Oh, and I felt the need to point this out:
If you have and you take natural logs of both sides, you take the log of the entire side i.e. and as you know, in general .2/x=e^y - e^-y
this is totally wrong but I do not know how to continue or to handle problem such as this one. Can any one give me a hint and direction about solving this problem?