Some "fragmented" Questions...

I'm thinking of making a maths library....(with algebra, calculus ..etc)..for using in other programs....
Some questions regarding the best way of implementation..
1. When I made an expression evaluator ...I used a deque of tokens(token==my class for storing the individual units..) for almost every operation on the expression.
Would it be a good idea to continue using it in case of equations ...for eg: Should I make a class containing two "deque<token>" s and use it as the equation or is there a better way?

2. Again, earlier ..I wrote my own parser for generating the deque from the raw input.
Would a regular expression tool or a lexical generator ..be significantly better than that ?

3. For solving equations , would a graphical method(evidently sacrificing some accuracy)...be a good alternative to algebraically solving them ?