# Proving Stirling's formula help

1. Nov 26, 2004

### Physicist

proving Stirling's formula.. help plz

How can I prove Stirling's formula?

n!= integral from 0 to inf. exp(-t) t^n dt= n^n exp(-n) (2 pi n)^0.5

there's a hint to use the substitution t=ny & ln(1+y) = y- 0.5 y^2

I tried to use it but I couldn't intgrate.. I tried integrating by parts but it became more complicated..

Can anyone help?

(How can I write the mathematical symbols here?)

Thanks

Last edited: Nov 26, 2004
2. Nov 26, 2004

### Andrew Mason

Try:
http://www.sosmath.com/calculus/sequence/stirling/stirling.html

AM

3. Nov 26, 2004

### Tide

Another approach would be to use the method of steepest descent. Basically, you can find where $t^n e^{-t}$ is a maximum and observe that the most significant contribution to the integral comes from near that maximum.

4. Nov 27, 2004

### Physicist

Thanks for helping.. but I should uuse the substitution t=ny..

HELP PLZ

5. Dec 3, 2004

6. Dec 3, 2004

### Physicist

Thanks alot..

7. Jan 5, 2012

### nafaa

Re: proving Stirling's formula.. help plz

How can I find equivalent Frenkel defects in the crystal through the equivalent Stralink

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