Difference between revisions of "009B Sample Midterm 1, Problem 4"

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<span class="exam">Evaluate the integral:
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<span class="exam"> Evaluate the indefinite and definite integrals.
  
::<math>\int \sin^3x \cos^2x~dx</math>
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<span class="exam">(a) &nbsp; <math>\int x^2 e^x~dx</math>
  
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<span class="exam">(b) &nbsp; <math>\int_{1}^{e} x^3\ln x~dx</math>
  
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!Foundations: &nbsp;
 
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|Recall the trig identity: <math style="vertical-align: -2px">\sin^2x+\cos^2x=1.</math>
 
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|How would you integrate <math style="vertical-align: -14px">\int \sin^2x\cos x~dx?</math>
 
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::You could use <math style="vertical-align: 0px">u</math>-substitution. Let <math style="vertical-align: -2px">u=\sin x.</math> Then, <math style="vertical-align: -1px">du=\cos x~dx.</math>
 
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::Thus, <math style="vertical-align: -14px">\int \sin^2x\cos x~dx\,=\,\int u^2~du\,=\,\frac{u^3}{3}+C\,=\,\frac{\sin^3x}{3}+C.</math>
 
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'''Solution:'''
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<hr>
{| class="mw-collapsible mw-collapsed" style = "text-align:left;"
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[[009B Sample Midterm 1, Problem 4 Solution|'''<u>Solution</u>''']]
!Step 1: &nbsp;
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|First, we write <math style="vertical-align: -13px">\int\sin^3x\cos^2x~dx=\int (\sin x) \sin^2x\cos^2x~dx</math>.
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[[009B Sample Midterm 1, Problem 4 Detailed Solution|'''<u>Detailed Solution</u>''']]
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|Using the identity <math style="vertical-align: -2px">\sin^2x+\cos^2x=1</math>, we get <math style="vertical-align: -1px">\sin^2x=1-\cos^2x</math>. If we use this identity, we have
 
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| &nbsp; &nbsp; <math style="vertical-align: -13px">\int\sin^3x\cos^2x~dx=\int (\sin x) (1-\cos^2x)\cos^2x~dx=\int (\cos^2x-\cos^4x)\sin(x)~dx</math>.
 
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!Step 2: &nbsp;
 
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|Now, we use <math style="vertical-align: 0px">u</math>-substitution. Let <math style="vertical-align: -5px">u=\cos(x)</math>. Then, <math style="vertical-align: -5px">du=-\sin(x)dx</math>. Therefore,
 
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| &nbsp;&nbsp; <math style="vertical-align: -14px">\int\sin^3x\cos^2x~dx=\int -(u^2-u^4)~du=\frac{-u^3}{3}+\frac{u^5}{5}+C=\frac{\cos^5x}{5}-\frac{\cos^3x}{3}+C</math>.
 
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{| class="mw-collapsible mw-collapsed" style = "text-align:left;"
 
!Final Answer: &nbsp;
 
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| &nbsp;&nbsp; <math>\frac{\cos^5x}{5}-\frac{\cos^3x}{3}+C</math>
 
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[[009B_Sample_Midterm_1|'''<u>Return to Sample Exam</u>''']]
 
[[009B_Sample_Midterm_1|'''<u>Return to Sample Exam</u>''']]

Latest revision as of 16:05, 12 November 2017

Evaluate the indefinite and definite integrals.

(a)  

(b)  



Solution


Detailed Solution


Return to Sample Exam