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Advanced Physics Homework Help
Stirlings approx/CoinFlips/Gamma function
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[QUOTE="thatguy14, post: 4663650, member: 223350"] [h2]Homework Statement [/h2] Hi I actually have three questions that I am posting here, help in all of them would be greatly appreciated! 1) Prove that ln(n!) ≈ nln(n)-n+ln(2*pi*n)/2 for large n 2)Supposed you flip 1000 coins, what is the probability of getting exactly 500 heads 3) Show that n! = [itex]\int x^{n}exp(-x)dx[/itex] where n is an integrer and the injtegral is from 0 to infinity. (The gamma function extends this definition of factorial to include non-integrers, z).[h2]Homework Equations[/h2] Below [h2]The Attempt at a Solution[/h2] 1) I am pretty lost here. This is a third year thermodynamics course (not been heavily math based so far) so the solution shouldn't be something above that level. I don't even know where to start. 2) This one I thought would be really easy (and it should be). This is what I did. I started off by ignoring the last term of stirlings approximation (this is what the textbook has and my prof did). the probability is P[itex]_{N}[/itex](n) = [itex]\frac{N!}{(N-n)!n!}[/itex]*2[itex]^{-N}[/itex] by using stirlings approximation, (first taking the natural log of both sides) and simplifying I got (and my professor) P = exp(NlnN - (N-n)ln(N-n)-nln(n)-Nln(2)) but when I plug in 1000 for N and 500 for n I keep getting 1 which I don't think is right. What am I doing wrong? 3)I tried to do an integration by parts on the right side but it leads to some undefined things (i.e. 0*infinity) so I am lost yet again. I thought that was just a definition, how do I show that? Thanks [/QUOTE]
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Stirlings approx/CoinFlips/Gamma function
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