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November 6th, 2016, 01:32 PM  #1 
Senior Member Joined: Feb 2014 Posts: 114 Thanks: 1  Problem with expected value in Geometric distribution
Hello, Could you explain red line in the below image? What we used derivative? Thanks 
November 6th, 2016, 03:12 PM  #2 
Senior Member Joined: Sep 2015 From: USA Posts: 2,406 Thanks: 1307 
what exactly don't you understand? can you recognize that $\dfrac{d}{dp}(1p)^n = n(1p)^{n1}$ ? 
November 6th, 2016, 09:32 PM  #3 
Senior Member Joined: Feb 2014 Posts: 114 Thanks: 1  
November 6th, 2016, 09:34 PM  #4 
Senior Member Joined: Sep 2015 From: USA Posts: 2,406 Thanks: 1307  the $p$ in $(1p)$ It really should have been 0 all along but since there was a factor of $n$ in the earlier expressions the 0th term was 0 and was left out. Last edited by romsek; November 6th, 2016 at 09:36 PM. 

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distribution, expected, geometric, problem 
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