My table of Integrals has the final scenario ##int frac dx x^2+a^2 ## as a 'standard' integral too, not merely the situation in which ##a=1##. But I do think this remaining a Calculus homework challenge it is expected with the OP to figure out how to make it happen. Hints https://gabletoppak.com/why-gable-top-cartons-are-making-a-splash-in-the-water-industry/