2/ Rút gọn tổng sau:
$C=\tfrac{C_{n}^{1}}{1}+2\tfrac{C_{n}^{2}}{C_{n}^{1}}+...+k\tfrac{C_{n}^{k}}{C_{n}^{k-1}}+...+n\tfrac{C_{n}^{n}}{C_{n}^{n-1}}$
Edited by moonlight0610, 03-09-2012 - 18:49.
Edited by moonlight0610, 03-09-2012 - 18:49.
Edited by NosoZ, 03-09-2012 - 16:09.
Edited by NosoZ, 03-09-2012 - 21:59.
Bài 1 có thể làm như sau1/ Chứng minh: $C_{2n+k}^{n}.C_{2n-k}^{n}\leqslant (C_{2n}^{n})^{2}$
Edited by Ispectorgadget, 07-09-2012 - 10:19.
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