Determine whether the given series converges absolutely$,$ converges conditionally, or diverges

a$){\displaystyle \underset{n=1}{\overset{}{}}}\frac{(-1{)}^n}{n^3+2}$

b$){\displaystyle \underset{n=1}{\overset{}{}}}\frac{(-1{)}^{n-1}}{2n-1}$