### Introduction

When you were first introduced to integration as the reverse of differentiation, the integrals you dealt with were
**
indefinite integrals
**
. The result of finding an indefinite integral is usually a function plus a constant of integration. In this Section we introduce
**
definite integrals
**
, so called because the result will be a definite answer, usually a number, with no constant of integration. Definite integrals have many applications, for example in finding areas bounded by curves, and finding volumes of solids.

#### Prerequisites

- understand integration as the reverse of differentiation
- be able to use a table of integrals

#### Learning Outcomes

- find simple definite integrals
- handle some integrals involving an infinite limit of integration

#### Contents

1 Definite integrals2 Evaluating definite integrals

3 Engineering Example 2

3.1 Torsion of a mild-steel bar

4 Some integrals with infinite limits