chapter 4ย ยท consider a partition ๐of the interval [ , ]into ๐subintervals by means of points...
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CHAPTER 4THE DEFINITE INTEGRAL
4.1 Introduction to Area
Area of Polygons
Area of a Region with a Curved Boundary
What is the area of a circle of radius 1? (Archimedes 287 BC)
Consider the regular inscribed polygons.
And the regular circumscribed polygons.
Sigma Notation
๐=1
๐
๐๐ = ๐1 + ๐2 +โฏ+ ๐๐
Some Examples
1. If ฯ๐=110 ๐๐ = 9 and ฯ๐=1
10 ๐๐ = 7, what are the values of ฯ๐=110 (3๐๐ โ 2๐๐) and ฯ๐=1
10 (๐๐ + 4) ?
2. Determine ฯ๐=1๐ (๐๐+1 โ ๐๐).
3. Determine the geometric sum ฯ๐=0๐ ๐๐๐.
Special Sum Formulas
Area of a Region with a Curved Boundary (revisited)What is the area of a circle of radius 1? (Archimedes 287 BC)
Consider the regular inscribed polygons.
And the regular circumscribed polygons.
Area of a Region Bounded by a Curve of a FunctionCalculate the area of the region under the curve ๐ฆ = ๐ฅ between 0 and 4.
Consider the region ๐ bounded by the parabola ๐ฆ = ๐ ๐ฅ = ๐ฅ2, the ๐ฅ-axis, and the vertical line ๐ฅ = 2.
Calculate its area ๐ด ๐ .
4.2 The Definite Integral
Riemann Sums
Consider a function ๐ defined on a closed interval [๐, ๐].
Consider a partition ๐ of the interval [๐, ๐] into ๐ subintervals by means of points ๐ = ๐ฅ0 < ๐ฅ1 < ๐ฅ2 < โฏ < ๐ฅ๐โ1 < ๐ฅ๐ = ๐ and let โ๐ฅ๐ = ๐ฅ๐ โ ๐ฅ๐โ1. On each subinterval [๐ฅ๐โ1, ๐ฅ๐], pick a sample point เดฅ๐ฅ๐ .
The sum ๐ ๐ = ฯ๐=1๐ ๐ เดฅ๐ฅ๐ โ๐ฅ๐ is called a Riemann sum for ๐
corresponding to the partition ๐.
Geometric Interpretation of Riemann Sum
The Definite Integral
Geometric Meaning of Definite Integral
What Functions are Integrable?
Calculating Definite Integral
Evaluate the given definite integrals using definition.
1. 02๐ฅ + 1 ๐๐ฅ .
2. 2โ1(2x + ฯ)๐๐ฅ .
Additive Property
Comparison Property
Boundedness Property
Linear Property
4.3 The First Fundamental Theorem of Calculus
Newton, Leibniz, and Calculus
www.calculusbook.net
Two Important Limits
Are these two limits related?
Distance and Velocity
Suppose that an object is traveling along the ๐ฅ-axis in such away that its velocity at time ๐ก is ๐ฃ = ๐ ๐ก feet per second. How far did it travel between ๐ก = 0 and ๐ก = 3?
The distance traveled is
lim๐โโ
ฯ๐=1๐ ๐ ๐ก๐ โ๐ก 0=
3๐ ๐ก ๐๐ก.
What about the distance ๐ traveled between ๐ก = 0 and ๐ก = ๐ฅ?
๐ ๐ฅ = เถฑ0
๐ฅ
๐ ๐ก ๐๐ก
What is the derivative of ๐ ?๐ โฒ(๐ฅ) = ๐ฃ = ๐(๐ฅ)
.
.
First Fundamental Theorem of Calculus
Examples.Find ๐บโฒ ๐ฅ .
(a) ๐บ ๐ฅ = 1๐ฅsin ๐ก ๐๐ก (b) ๐บ ๐ฅ = 1
๐ฅ2sin ๐ก ๐๐ก
(c) ๐บ ๐ฅ = sin ๐ฅ
co๐ ๐ฅsin ๐ก ๐๐ก (d) ๐บ ๐ฅ = 1
๐ฅ๐ฅ sin ๐ก ๐๐ก
Evaluating Definite Integral
Let ๐บ ๐ฅ = 0๐ฅsin ๐ก ๐๐ก.
1. Find ๐บ 0 .
2. Let ๐ฆ = ๐บ ๐ฅ , find ๐๐ฆ
๐๐ฅ.
3. Find the particular solution of the differential equation ๐๐ฆ
๐๐ฅ= sin ๐ฅ.
4. Use the result in 3. to find 0๐sin ๐ก ๐๐ก.
4.4 The Second Fundamental Theorem of Calculus
Second Fundamental Theorem of Calculus
Examples.
1. 4โโ2
๐ฆ2 +1
๐ฆ3๐๐ฆ .
2. ๐/6๐/2
2 sin ๐ก ๐๐ก .
Substitution Method
1. ๐ฅ ๐ฅ2 + 3โ12/7
๐๐ฅ .
2. ๐ฅ2 cos ๐ฅ3 + 5 ๐๐ฅ.
3. 14 ๐ฅโ1
3
๐ฅ๐๐ฅ .
4. 0๐/6
(sin ๐)3 cos ๐ ๐๐.
5. 01๐ฅ2 sin ๐ฅ3
2cos ๐ฅ3 ๐๐ฅ .
More Examples
๐ is a function that has a continuous third derivate. The dashed lines are tangent to the graph ๐ฆ = ๐(๐ฅ) at (1,1) and (5,1).
Tell whether the following integrals are positive, negative, or zero.
1. 15๐ ๐ฅ ๐๐ฅ.
2. 15๐โฒ ๐ฅ ๐๐ฅ.
3. 15๐โฒโฒ ๐ฅ ๐๐ฅ.
4. 15๐โฒโฒโฒ ๐ฅ ๐๐ฅ.
Water leaks out of a 55-gallon tank at the rate ๐โฒ ๐ก = 11 โ 1.1๐ก where ๐ก is measured in hours and ๐ in gallons. Initially the tank is full.1. How much water leaks out of the tank between ๐ก = 3 and ๐ก = 5 hours?2. How long does it take until there are just 5 gallons remaining in the tank?
4.5 The Mean Value Theorem for Integrals and the Use of Symmetry
Average Value of a Function
Do you still remember the Mean Value Theorem for Derivative?
If ๐ is integrable on the interval [๐, ๐], then the average value of ๐ on [๐, ๐] is:
If you consider the definite integral from over [๐, ๐] to be the area between the curve ๐(๐ฅ) and the ๐ฅ-axis, ๐๐๐ฃ๐ is the height of the rectangle that would be formed over that same interval containing precisely the same area.
b
a
ave dxxfab
f )(1
The Mean Value Theorem for Integrals
If ๐ is continuous on [๐, ๐], then there is a number ๐ between ๐ and ๐ such that
Example.
1. Suppose the temperature in degrees Celsius of a metal bar of length 2meters depends on the position ๐ฅ according to the function ๐(๐ฅ) =40 + 20๐ฅ(2 โ ๐ฅ). Find the average temperature in the bar. Is there a point where the actual temperature equals the average temperature.
2. Find all values of c that satisfy the Mean Value Theorem for ๐(๐ฅ) =|๐ฅ| on [โ2,2].
b
a
dttfab
cf )(1
)(
Symmetry Theorem
If ๐ is an even function then
If ๐ is an odd function, then
Periodicity
If ๐ is periodic with period ๐, then
Examples. Evaluate
1. .
2. .
3. .
4.6 Numerical Integration
Approximation of Definite Integral
If ๐ is continuous on a closed interval [๐, ๐], then the definite integral must exist. However, it is not always easy or possible to find the definite integral.
Examples.
เถฑsin ๐ฅ2 ๐๐ฅ
เถฑsin ๐ฅ
๐ฅ๐๐ฅ
In these cases, we use other methods to closely approximate the definite integral.
Methods
1. Left (or right or midpoint) Riemann sums
Estimate the area with rectangles
2. Trapezoidal Rule
Estimate the area with several trapezoids
3. Simpsonโs Rule
Estimate the area with the region contained under several parabolas
Left Riemann Sum
เถฑ๐
๐
๐ ๐ฅ ๐๐ฅ โ ๐ ๐ฅ0 + ๐ ๐ฅ1 +โฏ+ ๐(๐ฅ๐โ1) โ๐ฅ, โ๐ฅ =๐ โ ๐
๐
๐ธ๐ =๐ โ ๐ 2
2๐๐โฒ ๐ , for ๐ โค ๐ โค ๐
Right Riemann Sum
เถฑ๐
๐
๐ ๐ฅ ๐๐ฅ โ ๐ ๐ฅ1 + ๐ ๐ฅ2 +โฏ+ ๐(๐ฅ๐) โ๐ฅ, โ๐ฅ =๐ โ ๐
๐
๐ธ๐ = โ๐ โ ๐ 2
2๐๐โฒ ๐ , for ๐ โค ๐ โค ๐
Midpoint Riemann Sum
เถฑ๐
๐
๐ ๐ฅ ๐๐ฅ โ ๐๐ฅ0 + ๐ฅ1
2+ ๐
๐ฅ1 + ๐ฅ22
+โฏ+ ๐๐ฅ๐โ1 + ๐ฅ๐
2โ๐ฅ, โ๐ฅ =
๐ โ ๐
๐
๐ธ๐ =๐ โ ๐ 3
24๐2๐" ๐ , for ๐ โค ๐ โค ๐
Trapezoidal Rule
เถฑ๐
๐
๐ ๐ฅ ๐๐ฅ โโ๐ฅ
2๐ ๐ฅ0 + 2๐ ๐ฅ1 + 2๐ ๐ฅ2 +โฏ+ 2๐(๐ฅ๐โ1) + ๐(๐ฅ๐) , โ๐ฅ =
๐ โ ๐
๐
๐ธ๐ = โ๐ โ ๐ 3
12๐2๐" ๐ , for ๐ โค ๐ โค ๐
Simpson Rule (for even ๐)
เถฑ๐
๐
๐ ๐ฅ ๐๐ฅ โโ๐ฅ
3๐ ๐ฅ0 + 4๐ ๐ฅ1 + 2๐ ๐ฅ2 + 4๐ ๐ฅ3 +โฏ+ 2๐(๐ฅ๐โ2) + 4๐(๐ฅ๐โ1) + ๐(๐ฅ๐) , โ๐ฅ =
๐ โ ๐
๐
๐ธ๐ = โ๐ โ ๐ 5
180๐4๐(4) ๐ , for ๐ โค ๐ โค ๐
Examples
1. Approximate 13 1
1+๐ฅ2๐๐ฅ by using left Riemann sum, trapezoidal rule, and
Simpson rule with ๐ = 4. Then determine a maximum of the absolute error.
2. Determine ๐ so that the trapezoidal rule will approximate 13 1
๐ฅ๐๐ฅ with an error
๐ธ๐ satisfying |๐ธ๐| โค 0.01.
3. Determine ๐ so that the Simpson rule will approximate 13 1
๐ฅ๐๐ฅ with an error
๐ธ๐ satisfying |๐ธ๐| โค 0.01.
4. On her way to work, Ani noted her speed every 3 minutes. The results are shown in the table below. How far did she drive?
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