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Discussion Overview

The discussion revolves around a set of homework questions related to multivariable calculus, specifically focusing on double integrals and the application of integration techniques. Participants are seeking assistance with problem-solving and clarification of concepts.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express frustration over difficulty in solving the homework questions.
  • There is a repeated mention of a minimum at \((2,-1)\) being a global minimum, though the context is unclear.
  • Participants discuss the integrand for a specific problem, questioning whether it should be \(e^{y^8}\) or \(e^{y^3}\), with some suggesting that the problem may have been miswritten.
  • One participant suggests that the order of integration should be swapped to facilitate solving the integral.
  • There are requests for sketches and visual aids to help understand the problems better.
  • Some participants indicate they are unsure about using exponential integrals and gamma functions, suggesting a lack of familiarity with these concepts in the context of their coursework.
  • There are mentions of using polar coordinates for one of the questions, indicating a method for solving the problem.
  • Participants share links to external resources, such as Wolfram Alpha, for additional help with the problems.
  • Several participants ask for reviews of their answers and express uncertainty about their correctness.

Areas of Agreement / Disagreement

There is no clear consensus on the correct approach to the problems, with multiple competing views on the integrand and the method of integration. Participants are collaboratively exploring different interpretations and solutions without reaching a definitive agreement.

Contextual Notes

Some participants note that the use of exponential integrals and gamma functions may exceed the scope of their current coursework, indicating potential limitations in their understanding of the material.

Who May Find This Useful

Students studying multivariable calculus or those seeking help with similar homework problems may find this discussion relevant.

ozgunozgur
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I am trying to solve these questions for hours :/

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Let's begin with the first problem...what have you tried so far?
 
MarkFL said:
Let's begin with the first problem...what have you tried so far?
 

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Yes, I agree with your finding of a minimum at \((2,-1)\). It is a global minimum. For the second problem, isn't the integrand:

$$e^{y^8}$$ ?
 
MarkFL said:
Yes, I agree with your finding of a minimum at \((2,-1)\). It is a global minimum. For the second problem, isn't the integrand:

$$e^{y^8}$$ ?
Ah sorry. My third question is true? And second is a bit problem.
 
MarkFL said:
Yes, I agree with your finding of a minimum at \((2,-1)\). It is a global minimum. For the second problem, isn't the integrand:

$$e^{y^8}$$ ?
Isn't it gamma function for 8y?
 
I did question 2. Is it true? Can you help me?
 

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Please help me for second question, I guess I have to draw a sketch. Can you draw it full?
 
Can you review my answer?
 

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  • #12
The use of exponential integral and gamma functions goes beyond what I was taught in Calc 2. We did multi-variable calculus in Calc 3, but still worked with elementary functions. I can't help you with this problem. Perhaps someone else can.
 
  • #13
Questions 1 and 3 are fairly straight forward applications of multivariable Calculus with elementary functions.
So I think question 2 must also be such a straight forward application.
Looks to me as if the question should read:
$$\int_0^1 \int_{\sqrt x}^1 \exp(y^3)\,dy\,dx=\,?$$
That is, with power $3$, and with the variables of integration swapped.
Now we can solve it by swapping the order of integration, which is likely intended. And yes, a graph may help.
 
  • #14
Klaas van Aarsen said:
Questions 1 and 3 are fairly straight forward applications of multivariable Calculus with elementary functions.
So I think question 2 must also be such a straight forward application.
Looks to me as if the question should read:
$$\int_0^1 \int_{\sqrt x}^1 \exp(y^3)\,dy\,dx=\,?$$
That is, with power $3$, and with the variables of integration swapped.
Now we can solve it by swapping the order of integration, which is likely intended. And yes, a graph may help.
I'm not skilled in this part. Please help continue.
 
  • #15
ozgunozgur said:
I'm not skilled in this part. Please help continue.
Please show an attempt to swap the order of integration.
Or otherwise give us a clue in some detail where you are stuck.
You should have an example in your textbook that shows how it is done.
If you can't find such an example, you might take a look at this example.
 
  • #16
Klaas van Aarsen said:
Please show an attempt to swap the order of integration.
Or otherwise give us a clue in some detail where you are stuck.
You should have an example in your textbook that shows how it is done.
If you can't find such an example, you might take a look at this example.
 

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  • #17
Now that Klaas has figured out what #2 is actually supposed to be, let's look first at the region over which we are to integrate:

mhb_0017.png


Reversing the order of integration, we may write:

$$I=\int_0^1\int_0^{y^2} e^{y^3}\,dx\,dy$$

Can you proceed?
 
  • #18
For question 3 we should use a switch to polar coordinates:
\begin{tikzpicture}
\filldraw[green!70,draw=gray] (0,0) circle (2.5);
\draw[help lines] (-3.2,-3.2) grid (3.2,3.2);
\draw[->] (-3.4,0) -- (3.4,0);
\draw[->] (0,-3.2) -- (0,3.2);
\draw foreach \i/\x in {-2.5/-a,2.5/a} { (\i,0) node[below] {$\x$} };
\draw foreach \i/\y in {-2.5/-a,2.5/a} { (0,\i) node[ left ] {$\y$} };
\end{tikzpicture}
\[ \iint_D (x^2+y^2)\,dA = \int_0^a \int_0^{2\pi} r^2 \cdot r\,d\theta \,dr \]
 
  • #19
Thank you very much.
https://ibb.co/0XxGrDr
https://ibb.co/ZKNtgZy
I rearranged I wonder if I wrote extra or are we going right?
 
  • #20
.
 
  • #21
I was sent the other solut. Can you edit these two solving. https://ibb.co/c6S7r8n
 
  • #22

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