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November 11th, 2013, 08:45 PM   #1
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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?
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November 12th, 2013, 08:04 AM   #2
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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?
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November 12th, 2013, 12:44 PM   #3
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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.
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November 12th, 2013, 07:39 PM   #4
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Re: Sum of this expression

Quote:
Originally Posted by AfroMike
, 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.
I don't know where you got the 2 from but here's what I'm doing. Maybe you can catch my mistake;

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November 14th, 2013, 05:54 AM   #5
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Re: Sum of this expression

Your mistake is that
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November 17th, 2013, 01:38 AM   #6
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Re: Sum of this expression

Quote:
Originally Posted by AfroMike
Your mistake is that
That doesn't even look like the expression I wrote down
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November 17th, 2013, 08:39 AM   #7
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Re: Sum of this expression

Sivela, you mean to say that within the past week you haven't even detected your error?
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November 18th, 2013, 06:55 PM   #8
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Re: Sum of this expression

Quote:
Originally Posted by AfroMike
Sivela, you mean to say that within the past week you haven't even detected your error?
That's beside the point. Your expression looks like nothing I wrote down.
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.
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November 19th, 2013, 06:07 AM   #9
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Re: Sum of this expression

Ok, Sivela. It appeared you were being adamant. I'll quote here where I detected your error
Quote:
Originally Posted by sivela
You must not take my remark to heart - rather be more observant. Cheers.
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