回複：5th grader math rocks! problem - r u smarter than a 5th grade

來源: hisch 於 2010-02-18 16:08:33 [] [舊帖] [給我悄悄話] 閱讀數 : (219 bytes)

Q=sum_{i=1,60}(3^i)=3/2*(3^60-1)=3/2*[3^(3*4*5)-1]
(1) Q=3/2*[(3^3)^20-1]=3/2*[((13*2)+1)^20-1] =13*n;
(2) Q=3/2*[(3^4)^15-1]=3/2*[(5*2^4+1)^15-1]=5*3*2^3*m;
(3) Q=3/2*[(3^5)^12-1]=3/2*[(2*11^2+1)^12-1]=11^2*k;

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• Different Proof -hisch- ♂ 給 hisch 發送悄悄話 (0 bytes) () 02/18/2010 postreply 16:10:06

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