Definite integral is an important concept in high school mathematics and the basis of calculus. There are many methods to calculate definite integral, including method of substitution, integration by parts and pinch theorem. But definite integral also has some difficult concepts, such as the relationship between indefinite integral and definite integral, Newton Leibniz formula and so on.

There is a close relationship between indefinite integral and definite integral. The indefinite integral is the original function of the function, and the definite integral is the area or distance of the function in a certain interval. So we can use indefinite integral to calculate the original function of a function, and then use definite integral to calculate the area or distance of this function in a certain interval.

Newton Leibniz formula is an important formula in calculus, which describes the relationship between definite integral and indefinite integral. According to Newton's Leibniz formula, if a function f(x) is continuous in the interval [a, b], then its definite integral in the interval is equal to its indefinite integral in the interval plus two constants C 1 and C2. This formula is very important because it provides us with a method to find definite integral.

In a word, definite integral is a very complicated and important concept. Although it has some difficulties, we can understand and use it well as long as we study and master the related concepts and methods seriously.