Possible Duplicate:
$x^x=y$. How to solve for $x$?
If we have $x^x=4$ it's easily solved by substituting $x$ with $2$. But for general equation like $x^x = k$, how we can find the solution?
Moreover, what if we have equation $x^{a+bx}=k$ or $x^{f(x)}=k$