In the expansion of ${\left( {x – \frac{1}{x}} \right)^6}$, the constant term is

If the ${(r + 1)^{th}}$ term in the expansion of ${\left( {\sqrt[3]{{\frac{a}{{\sqrt b }}}} + \sqrt {\frac{b}{{\sqrt[3]{a}}}} } \right)^{21}}$ has the same power of $a$ and $b$, then the value of $r$ is

If coefficients of $2^{nd}$, $3^{rd}$ and $4^{th}$ terms in the binomial expansion of ${(1 + x)^n}$ are in $A.P.$, then ${n^2} – 9n$ is equal to

In the expansion of ${\left( {\frac{{3{x^2}}}{2} – \frac{1}{{3x}}} \right)^9}$,the term independent of $x$ is

Expand using Binomial Theorem $\left(1+\frac{ x }{2}-\frac{2}{ x }\right)^{4}, x \neq 0$