If $\frac{1}{n+1} {}^{n}C_{n} + \frac{1}{n} {}^{n}C_{n-1} + \dots + \frac{1}{2} {}^{n}C_{1} + {}^{n}C_{0} = \frac{1023}{10}$,then $n$ is equal to

If $P_{n}$ denotes the product of the binomial coefficients in the expansion of $(1+x)^{n}$,then $\frac{P_{n+1}}{P_n}=$

For $z \in \mathbb{C}$,if $(1+z)^n = 1 + { }^n C_1 z + { }^n C_2 z^2 + \ldots + { }^n C_n z^n$ and $\sum_{r=0}^{100} { }^{100} C_r \sin(rx) = \left(2 \cos \frac{x}{2}\right)^{100} \sin(kx)$,then $k =$

The value of $-{ }^{15}C_{1} 2 \cdot { }^{15}C_{2} - 3 \cdot { }^{15}C_{3} \ldots - 15 \cdot { }^{15}C_{15} { }^{14}C_{1} { }^{14}C_{3} { }^{14}C_{5} \ldots { }^{14}C_{11}$ is

$\sum_{k=0}^{20} \left({}^{20}C_{k}\right)^{2}$ is equal to :

$\binom{10}{1} + \binom{10}{2} + \binom{11}{3} + \binom{12}{4} + \binom{13}{5} = \dots$