$3\mathrm{.}8$ Frercises $3.$

Find the complex velocity potential for each of the following two dimensional irrotational incompressible flows.

$($a$)u=kx,v=-ky$

$($b$)u=\frac{kz}{x^2+y^2},v=\frac{ky}{x^2+y^2}$

where $k$ is a constant.