Evaluate the surface integral of a vector v=xi + yj+ zk over the closed surface of a cylinder w the circular base of radius a in the x-y plane and length h alon

dear, unit vector in z direction and -z direction.... but we consider origin of coordinates on bottom so hight of cylinder in bottom surface is Zero and Upper is h hight.... so we ...

dear unit vector equals to vector dil vided by its magnitude

hope you got it