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sai
Joined: 01 May 2004Posts: 2
Location: HK
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Posted: Sat May 01, 2004 12:04 pm Post subject: sum
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a+(a+1)r+(a+2)r^2+…+(a+n-1)r^(n-1)=?
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Peter
Frequent VisitorJoined: 18 Jan 2004Posts: 128
Location: Hong Kong
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Posted: Sat May 01, 2004 3:50 pm Post subject: Re: sum
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If , then the required sum is equal to .
For , write
.
The first sum can be readily found to be .
The second sum may be found by differentiation, yet you may proceed as follows:
. Therefore the required sum
._________________
Therefore do not worry about tomorrow, for tomorrow will worry about itself. Each day has enough trouble of its own.
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sai
Joined: 01 May 2004Posts: 2
Location: HK
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Posted: Sat May 01, 2004 6:20 pm Post subject:
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thx
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