4. Limit of a Riemann Sum
Write an expression for each of the following quantities:
1. the number of rectangles.
2. the width of each rectangle.
3. the height of each rectangle.
4. the area of each rectangle.
5. the total area of all rectangles.
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5. Limit of a Riemann Sum
Write an expression for each of the following quantities:
1. the number of rectangles. n
2. the width of each rectangle. ∆x = b−a
n
3. the height of each rectangle. f(xk)
4. the area of each rectangle. f(xk)∆x
5. the total area of all rectangles.
n
Í
k=1
f(xk)∆x
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6. Limit of a Riemann Sum
x1 = a + ∆x
x2 =
x3 =
.
.
.
xk =
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7. Limit of a Riemann Sum
x1 = a + ∆x
x2 = a + 2∆x
x3 = a + 3∆x
.
.
.
xk = a + k∆x
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8. Definite Integral as the Limit of a Riemann Sum
Definition of Definite Integral
If f is a continuous function defined on [a,b], and if:
• [a,b] is divided into n equal subintervals of width ∆x = b−a
n
,
• and if xk = a + k∆x is the right endpoint of subinterval k,
then the definite integral of f from a to b is the number
b
∫
a
f(x) dx = lim
n→∞
n
Õ
k=1
f(xk) ∆x
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9. Definite Integral as the Limit of a Riemann Sum
Let n be the number of subintervals. The
exact area under the curve is given by the
limit:
lim
n→∞
n
Í
k=1
5
n
5k
n
2
+ 2
lim
n→∞
n
Í
k=1
5k
n
2
+ 2
∆x
which is exactly equal to:
5
∫
0
(x2
+ 2) dx
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10. Definite Integral as the Limit of a Riemann Sum
Which of the following limits is equal to
5
∫
3
x4
dx?
(A) lim
n→∞
n
Í
k=1
3 + k
n
4
1
n
(B) lim
n→∞
n
Í
k=1
3 + k
n
4
2
n
(C) lim
n→∞
n
Í
k=1
3 + 2k
n
4
1
n
(D) lim
n→∞
n
Í
k=1
3 + 2k
n
4
2
n
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11. Definite Integral as the Limit of a Riemann Sum
Which of the following limits is equal to
5
∫
3
x4
dx?
(A) lim
n→∞
n
Í
k=1
3 + k
n
4
1
n
(B) lim
n→∞
n
Í
k=1
3 + k
n
4
2
n
(C) lim
n→∞
n
Í
k=1
3 + 2k
n
4
1
n
(D) lim
n→∞
n
Í
k=1
3 + 2k
n
4
2
n
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12. Definite Integral as the Limit of a Riemann Sum
Which of the following limits is equal to
5
∫
2
(4 − 2x) dx?
(A) lim
n→∞
n
Í
k=1
4 − 2
2 + k
n
1
n
(B) lim
n→∞
n
Í
k=1
4 − 2
2 + 3k
n
1
n
(C) lim
n→∞
n
Í
k=1
4 − 2
2 + k
n
3
n
(D) lim
n→∞
n
Í
k=1
4 − 2
2 + 3k
n
3
n
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13. Definite Integral as the Limit of a Riemann Sum
Which of the following limits is equal to
5
∫
2
(4 − 2x) dx?
(A) lim
n→∞
n
Í
k=1
4 − 2
2 + k
n
1
n
(B) lim
n→∞
n
Í
k=1
4 − 2
2 + 3k
n
1
n
(C) lim
n→∞
n
Í
k=1
4 − 2
2 + k
n
3
n
(D) lim
n→∞
n
Í
k=1
4 − 2
2 + 3k
n
4
3
n
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14. Summation Properties
Recall the following summation properties:
1.
n
Í
k=1
c =
2.
n
Í
k=1
cak =
3.
n
Í
k=1
(ak ± bk) =
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15. Summation Properties
Recall the following summation properties:
1.
n
Í
k=1
c = nc
2.
n
Í
k=1
cak = c
n
Í
k=1
ak
3.
n
Í
k=1
(ak ± bk) =
n
Í
k=1
ak ±
n
Í
k=1
bk
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16. Summation Formulas
Recall the following summation formulas:
1.
n
Í
k=1
k =
n(n + 1)
2
2.
n
Í
k=1
k2
=
n(n + 1)(2n + 1)
6
3.
n
Í
k=1
k3
=
n2
(n + 1)2
4
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17. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 5
3
(3x + 1) dx.
First, we write an expression for ∆x.
∆x =
Second, we write an expression for xk.
xk =
Third, we write the limit definition of the definite integral.
∫ 5
3
(3x + 1) dx =
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18. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 5
3
(3x + 1) dx.
First, we write an expression for ∆x.
∆x =
2
n
Second, we write an expression for xk.
xk = 3 +
2k
n
Third, we write the limit definition of the definite integral.
∫ 5
3
(3x + 1) dx = lim
n→∞
n
Õ
k=1
[3(xk) + 1] ∆x
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19. Limit Definition of Definite Integral
∫ 5
3
(3x + 1) dx = lim
n→∞
n
Õ
k=1
[3(xk) + 1] ∆x
= lim
n→∞
n
Õ
k=1
3
3 +
2k
n
+ 1
2
n
= lim
n→∞
n
Õ
k=1
20
n
+
12k
n2
= lim
n→∞
20
n
n
Õ
k=1
1 +
12
n2
n
Õ
k=1
k
#
= lim
n→∞
20
n
· n +
12
n2
·
n(n + 1)
2
= 20 + 6
= 26
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20. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 4
0
(2x2
+ 3) dx.
First, we write an expression for ∆x.
∆x =
Second, we write an expression for xk.
xk =
Third, we write the limit definition of the definite integral.
∫ 4
0
(2x2
+ 3) dx =
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21. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 4
0
(2x2
+ 3) dx.
First, we write an expression for ∆x.
∆x =
4
n
Second, we write an expression for xk.
xk =
4k
n
Third, we write the limit definition of the definite integral.
∫ 4
0
(2x2
+ 3) dx = lim
n→∞
n
Õ
k=1
[2(xk)2
+ 3] ∆x
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22. Limit Definition of Definite Integral
∫ 4
0
(2x2
+ 3) dx = lim
n→∞
n
Õ
k=1
[2(xk)2
+ 3] ∆x
= lim
n→∞
n
Õ
k=1
2
4k
n
2
+ 3
#
4
n
= lim
n→∞
n
Õ
k=1
128
n3
k2
+
12
n
= lim
n→∞
128
n3
n
Õ
k=1
k2
+
12
n
n
Õ
k=1
1
#
= lim
n→∞
128
n3
·
n(n + 1)(2n + 1)
6
+
12
n
· n
=
128
3
+ 12 =
164
3
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23. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 5
2
(8x − x2
) dx.
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24. Limit Definition of Definite Integral
Use the definition of definite integral to evaluate
∫ 5
2
(8x − x2
) dx. 45
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25. Credits
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