If the expansion in powers of $x$ of the function $\frac{1}{{\left( {1 - ax} \right)\left( {1 - bx} \right)}}$ is ${a_0} + {a_1}x + {a_2}{x^2} + \;{a_3}{x^3} + \; \ldots......$ then ${a_n}$ is
$\frac{{{b^n} - {a^n}}}{{b - a}}$
$\;\frac{{{a^n} - {b^n}}}{{b - a}}$
$\;\frac{{{a^{n + 1}} - {b^{n + 1}}}}{{b - a}}$
$\;\frac{{{b^{n + 1}} - {a^{n + 1}}}}{{b - a}}$
If ${S_n} = \sum\limits_{r = 0}^n {\frac{1}{{^n{C_r}}}} $ and ${t_n} = \sum\limits_{r = 0}^n {\frac{r}{{^n{C_r}}}} $, then $\frac{{{t_n}}}{{{S_n}}}$ is equal to
In the expansion of ${(1 + x)^5}$, the sum of the coefficient of the terms is
The value of $^{4n}{C_0}{ + ^{4n}}{C_4}{ + ^{4n}}{C_8} + ....{ + ^{4n}}{C_{4n}}$ is
What is the sum of the coefficients of ${({x^2} - x - 1)^{99}}$
The coefficient of $x^8$ in the expansion of $(x-1) (x- 2) (x-3)...............(x-10)$ is :