Probability - u substitution to find gamma function.

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SUMMARY

The forum discussion centers on the evaluation of the integral \(\int_0^∞ x^2 e^{-x/2} dx\) using u-substitution. The user initially applies the substitution \(u = x/2\) and calculates the integral as \(8 \Gamma(3)\), mistakenly equating \(\Gamma(3)\) to \(3!\). The correct evaluation reveals that \(\Gamma(3) = 2!\), leading to the accurate result of 16. This highlights the importance of correctly identifying the gamma function values in integral calculations.

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  • Understanding of u-substitution in integral calculus
  • Familiarity with the gamma function and its properties
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Homework Statement



\int_0^∞ x^2exp(-x/2) dx

Homework Equations



afe9f86ae39cdf0260aad124aac4a3e9.png


The Attempt at a Solution



Using u substitution:

u = x/2
du = 1/2 dx

\int_0^∞ 4u^2exp(-u) du*2
= 8 \Gamma(3)
= 8*3!
= 48

But the correct answer is 16 when I plug it in Wolfram's definite integral calculator. I don't see where's my mistake?

Thank you very much!
 
Physics news on Phys.org
Wow, Gamma(3) = 2!, not 3!. Silly me! Thanks anyways.
 

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