$2{C_0} + \frac{{{2^2}}}{2}{C_1} + \frac{{{2^3}}}{3}{C_2} + …. + \frac{{{2^{11}}}}{{11}}{C_{10}}$=

यदि $\sum_{ r =0}^{25}\left\{{ }^{50} C _{ r } \cdot{ }^{50- r } C _{25- r }\right\}= K \left({ }^{50} C _{25}\right)$ हो, तो $K$ का मान होगा

यदि ${a_k} = \frac{1}{{k(k + 1)}},$ जबकि $k = 1,\,2,\,3,\,4,…..,\,n$, तब ${\left( {\sum\limits_{k = 1}^n {{a_k}} } \right)^2} = $

$\left( {\left( {\begin{array}{*{20}{c}}
{21}\\
1
\end{array}} \right) – \left( {\begin{array}{*{20}{c}}
{10}\\
1
\end{array}} \right)} \right) + \left( {\left( {\begin{array}{*{20}{c}}
{21}\\
2
\end{array}} \right) – \left( {\begin{array}{*{20}{c}}
{10}\\
2
\end{array}} \right)} \right)$$ + \left( {\left( {\begin{array}{*{20}{c}}
{21}\\
3
\end{array}} \right) – \left( {\begin{array}{*{20}{c}}
{10}\\
3
\end{array}} \right)} \right) + \;.\;.\;.$$ + \left( {\left( {\begin{array}{*{20}{c}}
{21}\\
{10}
\end{array}} \right) – \left( {\begin{array}{*{20}{c}}
{10}\\
{10}
\end{array}} \right)} \right)$ का मान है:

यदि $1+\left(2+{ }^{49} C _1+{ }^{49} C _2+\ldots \ldots+{ }^{49} C _{49}\right)\left({ }^{50} C _2+\right.$ $\left.{ }^{50} C _4+\ldots . .+{ }^{50} C _{50}\right)=2^{ n } . m$ है, जहाँ $m$ एक विषम संख्या है, तो $n + m$ बराबर है $……….$