Hardly. It's a simple equation that has been independently discovered for as long as we've had algebra.

That's not the same as being obvious. Obvious means clear at first sight, or clear to a child. If you have to work for it, it's not obvious.

It was clear to me as a child of maybe 8. Granted, in this day and age it's much easier to come up with elementary math, but I would say that particular equation meets the obviousness criterion of patent law, based on the aforementioned historical evidence.