What is the fundamental theorem of calculus? I would remember my professors back in the day when proving a new concept they would say “by the fundamental theorem of calculus” at the end of the proof but I never really tried to dig deeper into that. I’m way beyond calc. I’m a math/Econ major taking abstract algebra and real analysis. Last calc class I took was diff eq over a year ago but I still don’t know what the fundamental theorem of calculus is.