a Evaluate ${\displaystyle \underset{c}{\overset{\phantom{}}{}}}\frac{z^2+1}{(z-3{)}^3}dz,$ where $C$ is a circle whose equation is $|z-2|=2$ in clockwise direction.

b Evaluate ${\displaystyle \underset{c}{\overset{\phantom{}}{}}}\frac{cosz}{z^2-1}dz,C$ :rectangle with vertices $+-2+-i.$