Find a value for:

$($a$)$

$(-\frac{5}{2})$

exactly

$($b$)$

${\displaystyle \underset{0}{\overset{0\mathrm{.}1}{}}}[\frac{sinx}{x}-\frac{1}{(1+x^2{)}^{\frac{3}{2}}}]dx$

up to ${10}^{-5}$