Cannot find my own mistake (derivation)

Hello.

So I have this:

which, in case and are positive, may be graphed like:

http://img44.imageshack.us/img44/8409/88706802.jpg

Assuming:

It seems plotting and should be essentially the same.

However, my real problem is when I try to get out of those equations.

*Unfortunately first pictures showing my thorough work had to be removed because of some reader-disruptive flaws.*

Essence of derivation of equation #1:

Essence of derivation of equation #2:

Why is there a big difference?