f(x) = x/x g(x) = 1 so... those are different functions? i dont know how to treat expressions like that. When expression is not defined for some x=a, but after some algebraic transformations i get expresion defined for x=a .... what happends? Can i make algebraic transformations on expressions with an unknown number without knowing it's value? I know can. But can i do this with epression that is part of a function?