Probability - u substitution to find gamma function.

sirhc1
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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!
 
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Wow, Gamma(3) = 2!, not 3!. Silly me! Thanks anyways.
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...

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