Yes, use the form eqn==0 (or lhs==rhs.) Your equations do not need to be defined as functions, but maybe if you can make some reasonable guesses for some of the parameters, something like this could help. Another idea for getting first guesses is if you can plausibly assume that some of the parameters are either really small or large and consider a slightly linearized version of the problem and get some estimates. Since it looks like your equations have algebraic non-linearities (unless I missed a term or something,) it should work out reasonably well with a little playing around. Hope that helps.