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