Solving a Double Integration Problem with Unknown Variables: How to Proceed?

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SUMMARY

The forum discussion centers on solving a double integration problem involving the integral $$\int\limits_{-2}^{\ 2} \ \int\limits_0^{\ \ \sqrt{4-x^2}} {x\over\sqrt{x^2+y^2} } \ dy \;dx$$. Participants suggest that the choice of substitution variable \( u = x^2 + y^2 \) is ineffective and recommend using polar coordinates instead. The discussion emphasizes the importance of understanding the geometric region of integration and the integrand's meaning, ultimately guiding the original poster toward a clearer path to the solution.

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  • Learn how to convert Cartesian coordinates to polar coordinates in integration
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  • #31
You answer the question
BvU said:
what ##\ x\over \sqrt{x^2 + y^2} ##represents
 
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  • #32
BvU said:
You answer the question
it has no meaning , right ? the author just simply put inside the equation, right ?
 
  • #33
You think I annoy you with so many questions when there is no meaning ? What is the sine of the red angle ? What is the cosine ?
upload_2016-9-12_13-46-56.png
 
  • #34
BvU said:
You think I annoy you with so many questions when there is no meaning ? What is the sine of the red angle ? What is the cosine ?
View attachment 105794
BvU said:
You answer the question
It's cos theta, so?
 
  • #35
chetzread said:
It's cos theta, so?

What do you think?
 
  • #36
@chetzread, I believe that BvU's hint is not about merely switching the order of integration (i.e., dxdy vs. dydx), but instead, about changing to a polar integral. This problem quite a bit easier if you do it this way.
 
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  • #37
chetzread said:
It's cos theta, so?
So ? Wouldn't substituting ##\theta## as integration variable be a sensible thing to try ?
 
  • #38
BvU said:
So ? Wouldn't substituting ##\theta## as integration variable be a sensible thing to try ?
ok, i got the ans now ...I'm wondering is this a special case? I have never learned and see this before ...
 
  • #39
Humor me and tell me what you did ...
 
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  • #40
BvU said:
Humor me and tell me what you did ...
 
  • #41
You said
chetzread said:
ok, i got the ans now
could you share your working with us ?
 

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