# Integral

## Definite Integrals, Indefinite IntegralsApplications

The integral is one of two main concepts embodied in the branch of **mathematics** known as **calculus**, and it corresponds to the area under the graph of a **function**. The area under a **curve** is approximated by a series of rectangles. As the number of these rectangles approaches **infinity**, the **approximation** approaches a limiting value, called the value of the integral. In this sense, the integral gives meaning to the concept of area, since it provides a means of determining the areas of those irregular figures whose areas cannot be calculated in any other way (such as by multiple applications of simple geometric formulas). When an integral represents an area, it is called a definite integral, because it has a definite numerical value.

The integral is also the inverse of the other main concept of calculus, the **derivative**, and thus provides a way of identifying functional relationships when only a **rate** of change is known. When an integral represents a function whose derivative is known, it is called an indefinite integral and is a function, not a number. Fermat, the great French mathematician, was probably the first to calculate areas by using the method of integration.

There are many applications in business, economics and the sciences, including all aspects of **engineering**, where the integral is of great practical importance. Finding the areas of irregular shapes, the volumes of solids of revolution, and the lengths of irregular shaped curves are important applications. In addition, integrals find application in the calculation of **energy** consumption, power usage, refrigeration requirements and innumerable other applications.

## Resources

### Books

Abbot, P., and M.E. Wardle. *Teach Yourself Calculus.* Lincolnwood, IL: NTC Publishing, 1992.

Larson, Ron. *Calculus With Analytic Geometry.* Boston: Houghton Mifflin College, 2002.

Weisstein, Eric W. *The CRC Concise Encyclopedia of Mathematics.* New York: CRC Press, 1998.

J.R. Maddocks

## Additional topics

Science EncyclopediaScience & Philosophy: *Incomplete dominance* to *Intuitionism*