Triple Integral: Is \[\frac{{x^3 }}{3}\] Right?

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Discussion Overview

The discussion revolves around evaluating a triple integral defined as \[ I = \int\limits_0^1 {\int\limits_0^x {\int\limits_0^y {ydzdydx} } } \] and whether the result is \[\frac{{x^3 }}{3}\]. Participants explore the steps involved in the integration process and express uncertainty about the final answer.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant initially proposes that the result of the integral is \[\frac{{x^3 }}{3}\], expressing uncertainty about this conclusion.
  • Another participant challenges this claim, stating that since there is an integral with respect to dx, the result cannot be a function of x and must instead be a number.
  • A third participant emphasizes the importance of treating variables correctly during integration, suggesting that different variables in the integrand should be treated as constants.
  • A later reply acknowledges a mistake and suggests a different answer of \[\frac{1}{12}\], providing detailed steps for the integration process.
  • Another participant confirms the revised answer, indicating agreement with the steps shown.

Areas of Agreement / Disagreement

Participants express disagreement regarding the correct evaluation of the integral, with multiple competing views on the final result. The discussion remains unresolved as different interpretations and calculations are presented.

Contextual Notes

Some participants highlight the importance of correctly identifying the variable of integration and the implications this has on the final result. There are also unresolved mathematical steps in the integration process that contribute to the differing conclusions.

the one
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hi everyone
the integral is :
\[<br /> I = \int\limits_0^1 {\int\limits_0^x {\int\limits_0^y {ydzdydx} } } <br /> \]
I'm not sure about the answer , but i think it'll be
\[<br /> \frac{{x^3 }}{3}<br /> \]
am i right ?
thanks
 
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Go back and learn the basics again. Since there is an integral with respect to dx, the result cannot possibly be a function of x. The result here must be a number. Did you forget to do the final integral?
 
As halls said, pay very close attention to what variable you are integrating with respect to. If you have a different variable within the integrand treat it as a constant both while integrating and evaluating.
 
I knew that i was wrong
 
Last edited:
I am not so sure about that. I got a different answer. Perhaps you want to show your steps?
 
Sorry , It'll be 1/12 (won't it ??)
\[<br /> \begin{array}{l}<br /> \int\limits_0^1 {\int\limits_0^x {\int\limits_0^y {ydzdydx = \int\limits_0^1 {\int\limits_0^x {\left( {\int\limits_0^y {ydz} } \right)} } } } } dydx = \int\limits_0^1 {\int\limits_0^x {y^2 } dydx} \\ <br /> = \int\limits_0^1 {\left( {\int\limits_0^x {y^2 dy} } \right)} dx = \int\limits_0^1 {\frac{{x^3 }}{3}} dx = \left( {\frac{{x^4 }}{{12}}} \right)_0^1 = \frac{1}{{12}} \\ <br /> \end{array}<br /> \]
Thanks
 
There you go.
 

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