1. 5.2 Definite Integrals and Areas.
The student will learn about:
the definition of the definite integral,
the fundamental theorem of calculus, and
some applications.

2. Introduction
We begin this section by calculating areas under curves, leading to a definition of the definite integral of a function.
The Fundamental Theorem of Integral Calculus then provides an easier way to calculate definite integrals using indefinite integrals.
Finally, we will illustrate the wide variety of applications of definite integrals.

3. Definite Integral as a Limit of a Sum.
The Definite Integral may be viewed as the area between the function and the x-axis.

4. APPROXIMATING AREA BY RECTANGLES
We may approximate the area under a curve Inscribing rectangles under it. Use rectangles with equal bases and with heights equal to the height of the curve at the left-hand edge of the rectangles.

5. Area Under a Curve
The following table gives the “rectangular approximation” for the area under the curve y = x 2 for 1 ≤ x ≤ 2, with a larger
numbers of rectangles.
The calculations were done on
a graphing calculator, rounding
answers to three decimal places.
# Rectangles
Sum of Areas 4 8 16 32 64
128
256
512
1024
2048

6. Those Responsible. Isaac Newton 1642 -1727
Gottfried Leibniz

7. Example 1
5 · 3 – 5 · 1 =
15 – 5 = 10
Make a drawing to confirm your answer.
0  x  4
- 1  y  6

8. Example 2 4 Make a drawing to confirm your answer. 0  x  4
Nice red box?

10. Fundamental Theorem of Calculus
If f is a continuous function on the closed interval [a, b] and F is any antiderivative of f, then

11. Evaluating Definite Integrals
By the fundamental theorem we can evaluate
Easily and exactly. We simply calculate

12. Definite Integral Properties

13. Example 3
9 - 0 = 9
0  x  4
- 2  y  10
Do you see the red box?

14. Example 4
There is that red box again?

15. Examples 5 This is a combination of the previous two problems
= 9 + (e 6)/2 – 1/3 – (e2)/2 =
What red box?

16. Numerical Integration on a Graphing Calculator
0  x  3
- 1  y  3
-1  x  6
- 0.2  y  0.5

17. Application
From past records a management services determined that the rate of increase in maintenance cost for an apartment building (in dollars per year) is given by M ’ (x) = 90x 2 + 5,000 where M is the total accumulated cost of maintenance for x years.
Write a definite integral that will give the total maintenance cost through the seventh year. Evaluate the integral.
30 x 3 + 5,000x
= 10, ,000 – 0 – 0
= $45,290

18. Total Cost of a Succession of Units
The following diagrams illustrate this idea. In each case, the curve represents a rate, and the area under the curve, given by the definite integral, gives the total accumulation at that rate.

19. FINDING TOTAL PRODUCTIVITY FROM A RATE
A technician can test computer chips at the rate of –3x2 + 18x + 15 chips per hour (for 0 ≤ x ≤ 6), where x is the number of hours after 9:00 a.m. How many chips can be tested between 10:00 a.m. and 1:00 p.m.?

20. Solution - N (t) = –3t t + 15
The total work accomplished is the integral of this rate from t = 1 (10 a.m.) to t = 4 (1 p.m.):
Use your calculator
= ( ) – ( ) = 117
That is, between 10 a.m. and 1 p.m., 117 chips can be tested.

21. Summary.
We can evaluate a definite integral by the fundamental theorem of calculus:

22. HW