# Definite Integrals

**Topics:**Integral, Riemann sum, Interval

**Pages:**4 (796 words)

**Published:**December 15, 2012

Section 5.2

OBJECTIVES: - be able to express the area under a curve as a definite integral and as a limit of Riemann sums

- be able to compute the area under a curve using a numerical integration procedure

- be able to make a connection with the definition of integration with the limit of a Riemann Sum

Sigma notation enables us to express a large sum in compact form: [pic]

The Greek capital letter [pic](sigma) stands for “sum.” The index k tells us where to begin the sum (at the number below the [pic]) and where to end (the number above). If the symbol [pic] appears above the [pic], it indicates that the terms go on indefinitely. [pic] is called the norm of the partition which is the biggest [pic] (interval)

Riemann Sum: A sum of the form [pic] where f is a continuous function on a closed interval [a, b]; [pic] is some point in, and [pic] the length of, the kth subinterval in some partition of [a, b].

Big Ideas of a Riemann Sum:

- the limit of a Riemann sum equals the definite integral

- rectangles approximate the region between the x-axis

and graph of the function

- A function and an interval are given, the interval is

partitioned, and the height of each rectangle can be

a value at any point in the subinterval

Negative area?

Because the function is not positive, a Riemann sum

does not represent a sum of areas of the rectangles.

It represents the sum of areas above the x-axis subtract

the sum of areas below the x-axis.

Area Under a Curve (as a Definite Integral)

If [pic] is nonnegative and integrable over a closed interval [a, b], then the area under the curve y = f(x) from a to b is the integral of f from a to b.[pic]

EX1: Evaluate each integral

EX1a: [pic]EX1b: [pic]

EX2: Use the graph of the integrand and areas to evaluate each integral. EX2a: [pic]EX2b: [pic]...

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