Defining functions on Casio 991ES Plus and 115ES Plus

[BINUBALL]

No, you can't.

You can define f(x) and g(x) in table mode. And can make table with function value in given range. But f(x) and g(x) can be used only in table mode. None of the menu can use them(f(x), g(x)).

BTW on the newer model 570/991CW, you can define function f(x) and g(x) with function key and use them in a solver.