Hi,
Mit z = a+bi
a),b)
$$\frac{1}{(3-i)^2} = \frac{1}{8-6i} = \frac{8+6i}{100} = \frac{2}{25} + \frac{3}{50}i$$
c)
$$|z| = \sqrt{a^2+b^2} = \sqrt{\left(\frac{2}{25}\right)^2 + \left(\frac{3}{50}\right)^2} = 0,1$$
d)
$$\arctan(\frac ba) = 36,87°$$
Güße