$(2n + 1) (2n + 3) (2n + 5) ....... (4n - 1)$ is equal to :
$\frac{{(4n)\,\,!}}{{{2^n}\,.\,\,(2n)\,\,!\,\,(2n)\,\,!}}$
$\frac{{(4n)\,\,!\,\,\,n\,\,!}}{{{2^n}\,.\,\,(2n)\,\,!\,\,(2n)\,\,!}}$
$\frac{{(4n)\,\,!\,\,\,n\,\,!}}{{(2n)\,\,!\,\,(2n)\,\,!}}$
$\frac{{(4n)\,\,!\,\,\,n\,\,!}}{{{2^n}\,\,!\,\,(2n)\,\,!}}$
If ${(1 + x - 2{x^2})^6} = 1 + {a_1}x + {a_2}{x^2} + .... + {a_{12}}{x^{12}}$, then the expression ${a_2} + {a_4} + {a_6} + .... + {a_{12}}$ has the value
$\sum\limits_{k = 0}^{10} {^{20}{C_k} = } $
In the expansion of ${(1 + x)^n}$ the sum of coefficients of odd powers of $x$ is
If $f(y) = 1 - (y - 1) + {(y - 1)^2} - {(y - 1)^{^3}} + ... - {(y - 1)^{17}},$ then the coefficient of $y^2$ in it is
The sum to $(n + 1)$ terms of the following series $\frac{{{C_0}}}{2} - \frac{{{C_1}}}{3} + \frac{{{C_2}}}{4} - \frac{{{C_3}}}{5} + $..... is