84 Improper Integrals · Investigate the following integral with your neighbor and answer the...
Transcript of 84 Improper Integrals · Investigate the following integral with your neighbor and answer the...
8.4 Improper integrals comp.notebook January 20, 2016
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84 Improper Integrals
Graph
Discuss in your groups whether or not this integral has a limit.
Given
Evaluate the limit for b=10,100,1000, 2000.
8.4 Improper integrals comp.notebook January 20, 2016
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Infinite Integration Limits
Integrals with infinite limits of integration are improper integrals.
(1) If f(x) is continuous on [a,∞), then
(2) If f(x) is continuous on (∞,b], then
(3) If f(x) is continuous on (∞,∞), then
c any real number.
In (1) and (2) the limit is finite if the improper integralCONVERGES, and the limit is the value of the improper integral.
If the limit fails to exist, the improper integral DIVERGES.
In part (3), the integral on the left hand side converges if both improper integrals on the right hand side converge, otherwise it DIVERGES, and has no value.
8.4 Improper integrals comp.notebook January 20, 2016
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EX. 1Express in terms of definite limits, and then
evaluate the integral.
Ex. 2 [1,∞)
Does converge or diverge?
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EX. 3 Partial Fractions
Evaluate or state that it diverges.
8.4 Improper integrals comp.notebook January 20, 2016
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EX. 4 Using L'Hopital's Rule
Evaluate or state that it diverges.
8.4 Improper integrals comp.notebook January 20, 2016
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EX. 5 (∞,∞)
Evaluate
8.4 Improper integrals comp.notebook January 20, 2016
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Improper integrals with infinite discontinuities
Integrals of functions that become infinite at a point within the interval of convergence are called IMPROPER INTEGRALS.
(1) If is continuous on (a,b], then
(2) If is continuous on [a,b) , then
(3) If is continuous on [a,c) ∪ (c,b], then
In (1) and (2) if the limit is FINITE, the integral CONVERGES and the limit is the value of the improper integral. Else it DIVERGES
In (3) the integral CONVERGES if both integrals on the right hand side have values, otherwise it DIVERGES.
8.4 Improper integrals comp.notebook January 20, 2016
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EX. 6 Discontinuities
Some improper integrals have vertical asymptotes infinite discontinuities.
Evaluate
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Ex. 7 Infinite Discontinuity at an End Point
Evaluate
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EXPLORATIONInvestigate the following integral with your neighbor and answer the questions that follow.
(1)Explain why these integrals are improper if p>0.(2)Show the integral diverges if p=1.(3)Show the integral diverges if p>1.(4)Show that the integral converges if 0<p<1.
8.4 Improper integrals comp.notebook January 20, 2016
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Test For Convergence
If we can’t evaluate an improper integral directly, we determine convergence. If it diverges bye, bye, we’re done. If it converges, hello, we can use numerical methods to approximate its value.
COMPARISON TEST
Let f and g be continuous on [a,∞) with 0≤f(x)≤g(x), then
(1)
(2)
8.4 Improper integrals comp.notebook January 20, 2016
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Ex. 8 Investigating Convergence
Does the integral converge?
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APPLICATIONS
EX. 9 Finding CircumferenceUse the arc length formula to show that the circumference of the circle x2 + y2 = 81 is 18π.
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Ex. 10 Finding the Volume of an Infinite Solid
Find the volume of the solid obtained by revolving the curve y=xex 0≤x<∞ about the xaxis.