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[ Last edited by feixiaolin on 2014-12-21 at 12:05 ]
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feixiaolin: ½ð±Ò+4 2014-12-21 14:52:07
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linda_nm(feixiaolin´ú·¢): ½ð±Ò+5 2014-12-21 14:51:48
Can you double check whether the third item is (1+a+a^2)^2 or not? If that's true, it will be the sum of squared geometric series. Should be not complicated. Good luck.

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feixiaolin: ½ð±Ò+4 2014-12-21 14:51:57
>> syms k
>> symsum(a^k,k,0,k)
ans =
a^(k+1)/(a-1)-1/(a-1)
>> factor(ans)
ans =
(a^(k+1)-1)/(a-1)
>> symsum((a^(k+1)-1)/(a-1),k,0,k)
ans =
-(-a^(k+1)*a+(k+1)*a-k-1)/(a-1)^2-a/(a-1)^2
>> factor(ans)
ans =
-(-a^(k+1)*a+k*a+2*a-k-1)/(a-1)^2
ÉÆ¶ñµ½Í·ÖÕÓб¨,È˼äÕýµÀÊDz×É£.
4Â¥2014-12-21 12:12:55
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