N
nijinoakira0988


Chứng minh:
\frac{nC0}{(n+2)C1}+\frac{nC1}{(n+3)C2}+...+\frac{nCn}{(2n+2)C(n+1)}=\frac{1}{2}
\frac{nC0}{(n+2)C1}+\frac{nC1}{(n+3)C2}+...+\frac{nCn}{(2n+2)C(n+1)}=\frac{1}{2}
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