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Double integration problem

  • Thread starter chetzread
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  • #26
BvU
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Pity you don't post your drawing ...
 
  • #27
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do u ask me to draw out ##x\over \sqrt{x^2 + y^2} ## ???
If so , i really dun know how to draw it out ....
 
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  • #28
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Pity you don't post your drawing ...
this one ?
 

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  • #29
BvU
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No, this one:

draw a point ##\ x,y \ ## and consider what ##\
x\over \sqrt{x^2 + y^2} ## represents
Since words fail me, I will try it with a picture:



upload_2016-9-12_12-24-12.png


[edit] your picture looks cute, but why do you set the ranges to -50,50 instead of x -2,2 and y 0,2 ?
 
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  • #30
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No, this one:



Since words fail me, I will try it with a picture:



View attachment 105789

[edit] your picture looks cute, but wht do you set the ranges to -50,50 instead of x -2,2 and y 0,2 ?
So, how to proceed from ur diagram?
 
  • #31
BvU
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You answer the question
what ##\ x\over \sqrt{x^2 + y^2} ##represents
 
  • #32
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You answer the question
it has no meaning , right ? the author just simply put inside the equation, right ?
 
  • #33
BvU
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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
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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
You answer the question
It's cos theta, so?
 
  • #35
Ray Vickson
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  • #36
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@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
BvU
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It's cos theta, so?
So ? Wouldn't substituting ##\theta## as integration variable be a sensible thing to try ?
 
  • #38
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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 learnt and see this before ...
 
  • #39
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Humor me and tell me what you did ...
 
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  • #41
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You said
ok, i got the ans now
could you share your working with us ?
 

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