Answer
(a) $r=\sqrt {a^2+b^2}$, $tan\theta=\frac{b}{a}$
(b) $z=r(cos\theta+i\cdot sin\theta)$
Work Step by Step
(a) The modulus of z is $r=\sqrt {a^2+b^2}$, and an argument of z is an angle $theta$ satisfying $tan\theta=\frac{b}{a}$
(b) We can express z in polar form as $z=r(cos\theta+i\cdot sin\theta)$ ...
