Newton was interested in the mathematics of motion. He discovered the branch of mathematics (fluxions) in which an unknown number keeps changing. The word fluxion came from the word flux, which means "constant changing or flowing." Today, it is called calculus and taught in high school and college. Using fluxions, Newton learned how to find the area under a curve called a hyperbola.

Here is an example of a  formula for finding the integral ( area under a curve).