In the expansion $$\left(\frac{1}{x}+x \sin x\right)^{10}, \quad$$ the co - efficient of $$6^{\text {th }}$$ term is equal to $$7 \frac{7}{8}$$, then the principal value of $$x$$ is

If the sum of the coefficients of the first three terms in the expansion of $$\left(x-\frac{a}{x^2}\right)^{12}, x \neq 0$$ is 559. Find the value of '$$a$$' if '$$a$$' belongs to positive integers

The coefficient of the third term in the expansion of $$\left(x^2-\frac{1}{4}\right)^n$$, when expanded in the descending power of $$x$$ is 31, then $$n$$ is

Using mathematical induction, the numbers $$a_n \delta$$ are defined by $$a_0=1, a_{n+1}=3 n^2+n+a_n, (n \geq 0)$$. Then, $$a_n$$ is equal to