The middle term in the expansion of ${\left( {x + \frac{1}{{2x}}} \right)^{2n}}$, is
$\frac{{1.3.5....(2n - 3)}}{{n!}}$
$\frac{{1.3.5....(2n - 1)}}{{n!}}$
$\frac{{1.3.5....(2n + 1)}}{{n!}}$
None of these
The coefficient of ${t^{24}}$ in the expansion of ${(1 + {t^2})^{12}}(1 + {t^{12}})\,(1 + {t^{24}})$ is
The term independent of $x$ in the expansion of ${\left( {{x^2} - \frac{1}{x}} \right)^9}$ is
If the co-efficient of $x^9$ in $\left(\alpha x^3+\frac{1}{\beta x}\right)^{11}$ and the co-efficient of $x^{-9}$ in $\left(\alpha x-\frac{1}{\beta x^3}\right)^{11}$ are equal, then $(\alpha \beta)^2$ is equal to $.............$.
Middle term in the expansion of ${(1 + 3x + 3{x^2} + {x^3})^6}$ is