Your function seem to have some strange symbols which I don't understand. Is it,
In that case the definition seem to be problematic since \(f(0)\) is not defined properly. \(f(0)\) should be a constant value whereas in the definition it's not.
Good. But the problem here is that the function is not defined at \(x=0\) properly. We know that,Well, my language is portuguese, i forgot the translate of symbols: sen^2(x) = sin^(x), arctg(x)=arctan(x)..
and in the exercise is sin^2(x) and not sec^2(x).