Solution to Double Integral Problem

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Discussion Overview

The discussion revolves around solving a double integral of the function \(x^2 + y^2\) over a specified region in the positive quadrant defined by the inequality \(x + y \leq 1\). Participants explore various approaches to the problem, express their results, and seek clarification on discrepancies between their findings and those in a textbook.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant requests help in solving the double integral and expresses confusion over the solution.
  • Another participant mentions obtaining an answer of \( \frac{2}{3} \), while a textbook states the answer is \( \frac{1}{6} \), indicating a potential error in their calculations.
  • Participants emphasize the need to see the work done to identify where the misunderstanding might lie.
  • There is a suggestion to use LaTeX for clarity in mathematical expressions, and an alternative method of sharing work through screenshots is proposed.
  • A participant describes the integration process and suggests that the symmetry of the region allows for flexibility in the order of integration.
  • One participant calculates the integral and arrives at \( \frac{5}{12} \), questioning the textbook's answer and the choice of integration order.
  • Another participant agrees with the \( \frac{5}{12} \) result and notes that the choice of integration order does not significantly affect the difficulty of the problem.

Areas of Agreement / Disagreement

Participants express differing results for the integral, with some obtaining \( \frac{2}{3} \) and others \( \frac{5}{12} \), while the textbook states \( \frac{1}{6} \). This indicates a lack of consensus on the correct answer and the reasoning behind the choice of integration order remains a point of inquiry.

Contextual Notes

Participants have not fully resolved the discrepancies in their results, and there are missing details regarding the assumptions made in their calculations. The discussion reflects varying levels of familiarity with the integration process and the use of mathematical notation.

TheArun
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I want the answer for this and how is it solved.
double integral(x2+y2 dxdy) over the region in pos quadrant for which x+y<=1.
 
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Re: iam new...i have a question...pls help.

Arun said:
I want the answer for this and how is it solved.
double integral(x2+y2 dxdy) over the region in pos quadrant for which x+y<=1.

Wellcome on MHB Arun!...

... did You make some attempt?...

Kind regards

$\chi$ $\sigma$
 
Re: iam new...i have a question...pls help.

ya...sure..tried many times...iam getting 2/3 as ans...but accd to text it is 1/6...dont know y iam wrong.
Btw thank for reply.
 
Re: iam new...i have a question...pls help.

Arun said:
ya...sure..tried many times...iam getting 2/3 as ans...but accd to text it is 1/6...dont know y iam wrong.
Btw thank for reply.

Hi Arun,

Welcome to MHB! :) Please use proper English here, meaning don't use lots of abbreviations like "ans" for "answer".

In order to help you we need to see what work you've done, so without seeing how you got $\frac{2}{3}$ we don't know where you went wrong.

Jameson
 
Re: iam new...i have a question...pls help.

Jameson said:
Hi Arun,

Welcome to MHB! :) Please use proper English here, meaning don't use lots of abbreviations like "ans" for "answer".

In order to help you we need to see what work you've done, so without seeing how you got $\frac{2}{3}$ we don't know where you went wrong.

Jameson

sorry fed up with all the subscripts and superscripts...is der some easier way...anyway i have done it in word.but it is showing invalid file.
 
Re: iam new...i have a question...pls help.

Arun said:
sorry fed up with all the subscripts and superscripts...is der some easier way...anyway i have done it in word.but it is showing invalid file.

We use Latex on MHB and have a http://www.mathhelpboards.com/f26/ that explains how to use it. Until you learn how to use Latex I suggest taking a screenshot of your work and uploading the image to TinyPic. Then you can post the picture here.

Here is an example of what $\LaTeX$ can do:

$$\int_0^{\infty}e^{-x^2}\,dx=\frac{\sqrt{\pi}}{2}$$
 
Re: iam new...i have a question...pls help.

Jameson said:
We use Latex on MHB and have a http://www.mathhelpboards.com/f26/ that explains how to use it. Until you learn how to use Latex I suggest taking a screenshot of your work and uploading the image to TinyPic. Then you can post the picture here.

Here is an example of what $\LaTeX$ can do:

$$\int_0^{\infty}e^{-x^2}\,dx=\frac{\sqrt{\pi}}{2}$$

this is the image
156966o.jpg
 
All right!... the region of integration is the 'colored area' of the figure...

http://www.123homepage.it/u/i69735807._szw380h285_.jpg.jfif

The symmetry respect to x and y is evident, so that we can choose one or the other order of integration and write...

$\displaystyle \int\int_{A} (x^{2} + y^{2})\ dy\ dx = \int_{0}^{1} dx\ \int_{0}^{1-x} (x^{2}+y^{2})\ dy = \int_{0}^{1} |x^{2}\ y + \frac{y^{3}}{3}|_{0}^{1-x}\ dx = \int_{0}^{1} (\frac{1}{3} - x + 2\ x^{2} - \frac{x^{3}}{3})\ dx$ (1)

Now are You able to proceed?...

Kind regards

$\chi$ $\sigma$
 
so it turns out to be 5/12 right...?
But answer in a text is shown to be 1/6...author's mistake is it?
And i would also like to know y u chose this order of integration is it easier this way...the logic?
A very big thanks.
 
  • #10
Arun said:
so it turns out to be 5/12 right...?
But answer in a text is shown to be 1/6...author's mistake is it?
And i would also like to know y u chose this order of integration is it easier this way...the logic?
A very big thanks.
Hello Arun,
I get it also to $$\frac{5}{12}$$ and about the order of integration both is same difficult/simple. You can try it out if you want.
edit: When you mean 'order of integration' I asume you mean why he did choose $$1-x$$ insted of $$1-y$$

Regards,
$$|\pi\rangle$$
 
Last edited:

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