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Integration with Trigonometric Substitution 
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#1
Mar208, 12:21 PM

P: 4

1. The problem statement, all variables and given/known data
Given integral (I): I[(x)sqrt(9x^2)dx] by words: Integral of "X" times square root of "9X(squared) Use proper trigonometric substitution to solve this problem. 2. Relevant equations 3. The attempt at a solution 


#2
Mar208, 12:29 PM

P: 1,754

You don't even need Trig substitution.
[tex]\int x\sqrt{9x^2}dx[/tex] [tex]u=9x^2[/tex] [tex]du=2xdx \rightarrow xdx=\frac 1 2 du[/tex] 


#3
Mar208, 12:31 PM

P: 4

I know that I don't need that.
But the problem is, I have to use it. The exercise require it. 


#4
Mar208, 01:21 PM

P: 1,754

Integration with Trigonometric Substitution
Well you posted the solution to it? I don't know what else to tell you. Just analyze what they did. Work it yourself a couple times if you have to.



#5
Mar208, 01:57 PM

P: 420

You forgot a term when you first did the substitution.
x = 3sin(u) dx = 3cos(u)du (9  x^2)^(1/2) = 3cos(u) So the integral becomes 27sin(u)cos^2(u)du 


#6
Mar308, 02:58 PM

P: 4

[tex]\int x^2\sqrt{9x^2}dx[/tex]
apropo [tex]u=x^2\sqrt{9x^2}dx[/tex] 


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