to use the integral test to prove the convergence or divergence of a given series, three conditions must be met, the first is it must be continuous, second, it must be positive, and third it must be decreasing...

I know how to determine number one and number three, but i havent been sure about how to determine or prove that the series is positive (or the function being used to integrate anyways), this should be simple and right under my nose since i cannot find the answer in any of my books, any insight? thanks