# Definite Integral

### Contents

page 1 of 2

Page 1

Page 2

#### Antiderivatives and the Fundamental Theorem of Calculus

In this section we present the fundamental theorem of calculus. First, we must make a definition. A function F(x) is called an antiderivative of a function f (x) if f (x) is the derivative of F(x); that is, if F'(x) = f (x). The antiderivative of a function f (x) is not unique, since adding a constant to a function does not change the value of its derivative:

 (f (x) + c) = (f (x)) + (c) =

It is true, however, that any two antiderivatives of a function f (x) will differ by a constant.

Why are antiderivatives a useful concept? Because they provide a shortcut for calculating definite integrals, as shown by the first part of the fundamental theorem of calculus.

#### Fundamental Theorem of Calculus 1

Let f (x) be a function that is integrable on the interval [a, b] and let F(x) be an antiderivative of f (x) (that is, F'(x) = f (x)). Then

 f (x)dx = F(b) - F(a)

Since the expression F(b) - F(a) is one we will encounter often, we will sometimes employ a special shorthand to simplify our equations:

 F(x)|ab = F(b) - F(a)

Note that any antiderivative F(x) will give the same value for F(b) - F(a), since any two antiderivatives differ only by a constant, which will cancel upon subtraction. The formula in the theorem may also be written

Page 1

Page 2