November 11th, 2013, 08:45 PM  #1 
Senior Member Joined: Jan 2009 Posts: 345 Thanks: 3  Sum of this expression
What's the summation of the following expression; The solution is said to But I'm getting . How is this possible? 
November 12th, 2013, 08:04 AM  #2 
Senior Member Joined: Feb 2013 Posts: 281 Thanks: 0  Re: Sum of this expression
My guesswork is that you didn't apply the geometrical progression formula corerctly. Did you consider that k starts with 1 instead of 0?

November 12th, 2013, 12:44 PM  #3 
Senior Member Joined: Dec 2012 Posts: 372 Thanks: 2  Re: Sum of this expression , where is the first term of the geometric series, is the number of terms of the series and is the common ratio. For your problem, . Plug these in the formula to convince yourself of the final answer.

November 12th, 2013, 07:39 PM  #4  
Senior Member Joined: Jan 2009 Posts: 345 Thanks: 3  Re: Sum of this expression Quote:
 
November 14th, 2013, 05:54 AM  #5 
Senior Member Joined: Dec 2012 Posts: 372 Thanks: 2  Re: Sum of this expression
Your mistake is that 
November 17th, 2013, 01:38 AM  #6  
Senior Member Joined: Jan 2009 Posts: 345 Thanks: 3  Re: Sum of this expression Quote:
 
November 17th, 2013, 08:39 AM  #7 
Senior Member Joined: Dec 2012 Posts: 372 Thanks: 2  Re: Sum of this expression
Sivela, you mean to say that within the past week you haven't even detected your error?

November 18th, 2013, 06:55 PM  #8  
Senior Member Joined: Jan 2009 Posts: 345 Thanks: 3  Re: Sum of this expression Quote:
My mistake was forgetting to multiply my result by 2, the first term as the formula shows. I don't know how you could have missed this.  
November 19th, 2013, 06:07 AM  #9  
Senior Member Joined: Dec 2012 Posts: 372 Thanks: 2  Re: Sum of this expression
Ok, Sivela. It appeared you were being adamant. I'll quote here where I detected your error Quote:
 

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