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Finding the area under a curve: Riemann, Trapezoidal, and Simpsons Rule Adguary Calwile Laura Rogers Autrey~ 2 nd Per. 3/14/11.

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Presentation on theme: "Finding the area under a curve: Riemann, Trapezoidal, and Simpsons Rule Adguary Calwile Laura Rogers Autrey~ 2 nd Per. 3/14/11."— Presentation transcript:

1 Finding the area under a curve: Riemann, Trapezoidal, and Simpsons Rule Adguary Calwile Laura Rogers Autrey~ 2 nd Per. 3/14/11

2 Introduction to area under a curve Before integration was developed, people found the area under curves by dividing the space beneath into rectangles, adding the area, and approximating the answer. As the number of rectangles, n, increases, so does the accuracy of the area approximation.

3 Introduction to area under a curve (cont.) There are three methods we can use to find the area under a curve: Riemann sums, the trapezoidal rule, and Simpsons rule. For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

4 Finding Area with Riemann Sums For convenience, the area of a partition is often divided into subintervals with equal width – in other words, the rectangles all have the same width. (see the diagram to the right for an example of a Right Riemann approximation)For convenience, the area of a partition is often divided into subintervals with equal width – in other words, the rectangles all have the same width. (see the diagram to the right for an example of a Right Riemann approximation) Subintervals with equal width

5 Finding Area with Riemann Sums It is possible to divide a region into different sized rectangles based on an algorithm or rule (see graph above)It is possible to divide a region into different sized rectangles based on an algorithm or rule (see graph above)

6 Riemann Sums There are three types of Riemann Sums Right Riemann: Left Riemann: Midpoint Riemann:

7 Right Riemann- Overview Right Riemann places the right point of the rectangles along the curve to find the area. The equation that is used for the RIGHT RIEMANN ALWAYS begins with: And ends with Within the brackets!

8 Right Riemann- Example Remember: Right Only Given this problem below, what all do we need to know in order to find the area under the curve using Right Riemann? 4 partitions

9 Right Riemann- Example For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

10 Right Riemann- Example

11 Right Riemann TRY ME! Volunteer :___________________ 4 Partitions

12 !Show All Your Work! n=4

13 Did You Get It Right? n=4

14 Left Riemann- Overview Left Riemann uses the left corners of rectangles and places them along the curve to find the area. The equation that is used for the LEFT RIEMANN ALWAYS begins with: And ends with Within the brackets!

15 Left Riemann- Example Remember: Left Only Given this problem below, what all do we need to know in order to find the area under the curve using Left Riemann? 4 partitions

16 Left Riemann- Example For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

17 Left Riemann- Example

18 Left Riemann- TRY ME! Volunteer:___________ 3 Partitions

19 !Show All Your Work! n=3

20 Did You Get My Answer? n=3

21 Midpoint Riemann- Overview Midpoint Riemann uses the midpoint of the rectangles and places them along the curve to find the area. The equation that is used for MIDPOINT RIEMANN ALWAYS begins with: And ends with Within the brackets!

22 Midpoint Riemann- Example Remember: Midpoint Only Given this problem below, what all do we need to know in order to find the area under the curve using Midpoint Riemann? 4 partitions

23 Midpoint Riemann- Example For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

24 Midpoint Riemann- Example

25 Midpoint Riemann- TRY ME 6 partitions Volunteer:_________

26 !Show Your Work! n=6

27 Correct??? n=6

28 Goldstein/SCHNIEDER/LAY, CALCULUS AND ITS APPLICATIONS, 11e – Slide #26 Applications of Approximating AreasEXAMPLE SOLUTION The velocity of a car (in feet per second) is recorded from the speedometer every 10 seconds, beginning 5 seconds after the car starts to move. See Table 2. Use a Riemann sum to estimate the distance the car travels during the first 60 seconds. (Note: Each velocity is given at the middle of a 10-second interval. The first interval extends from 0 to 10, and so on.) Since measurements of the cars velocity were taken every ten seconds, we will use. Now, upon seeing the graph of the cars velocity, we can construct a Riemann sum to estimate how far the car traveled.

29 Goldstein/SCHNIEDER/LAY, CALCULUS AND ITS APPLICATIONS, 11e – Slide #27 Applications of Approximating Areas This is an example of using a midpoint Riemann sum to approximate an integral.

30 Goldstein/SCHNIEDER/LAY, CALCULUS AND ITS APPLICATIONS, 11e – Slide #28 Applications of Approximating Areas Therefore, we estimate that the distance the car traveled is 2800 feet. CONTINUED

31 Trapezoidal Rule Overview Trapezoidal Rule is a little more accurate than Riemann Sums because it uses trapezoids instead of rectangles. You have to know the same 3 things as Riemann but the equation that is used for TRAPEZOIDAL RULE ALWAYS begins with: and ends with Within the brackets with every f being multiplied by 2 EXCEPT for the first and last terms

32 Trapezoidal Rule- Example Remember: Trapezoidal Rule Only Given this problem below, what all do we need to know in order to find the area under the curve using Trapezoidal Rule? 4 partitions

33 Trapezoidal Example For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

34 Trapezoidal Rule- Example

35 Trapezoidal Rule- TRY Me Volunteer:_____________ 4 Partitions

36 Trapezoidal Rule- TRY ME!! n=4

37 Was this your answer? n=4

38 Simpsons Rule- Overview Simpsons rule is the most accurate method of finding the area under a curve. It is better than the trapezoidal rule because instead of using straight lines to model the curve, it uses parabolic arches to approximate each part of the curve. The equation that is used for Simpsons Rule ALWAYS begins with: And ends with Within the brackets with every f being multiplied by alternating coefficients of 4 and 2 EXCEPT the first and last terms. In Simpsons Rule, n MUST be even.

39 Simpsons Rule- Example Remember: Simpsons Rule Only Given this problem below, what all do we need to know in order to find the area under the curve using Simpsons Rule? 4 Partitions

40 Simpsons Example For each method we must know: f(x)- the function of the curve n- the number of partitions or rectangles (a, b)- the boundaries on the x-axis between which we are finding the area

41 Simpsons Rule- Example

42 Simpsons Rule TRY ME! 4 partitions Volunteer:____________

43 !Show Your Work! n=4

44 Check Your Answer!

45 Sources © Laura Rogers, Adguary Calwile; 2011


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