Newton-Leibniz formula is a mathematical expression of the reciprocal relationship between differential and integral. According to this formula, if the function f(x) is continuous in the closed interval [a, b] and f(x) is the original function of f(x), then the definite integral of F(x) in [a, b] is equal to the difference between the function values of F(x) at b and a, that is, ∫ (a → b). This means that by integrating the function f(x), we can get its original function F(x), and by differentiating, we can get the function F(x). This reflects the relationship between differential and integral.