The coefficient of middle term in the expansion of $(1+{x})^{40}$ is

The value of the sum $\sum _{ j=0 }^{ 8 }{8 \choose j}{ \frac { 1 }{ (j+1)(j+2) } }$ is

The number of terms in the expansion of $\left\{ ( \sqrt {2}x +\sqrt {3} y)^{10} - ( \sqrt {2} x - \sqrt {3} y)^{10} \right\}$ is-

দৃশ্যকল্প- $: f(\mathrm{y})=\mathrm{y}-1$.

দৃশ্যকল্প-২ : $(1+a y)^{m}$ একটি দ্বিপদী রাশি।