I need help with numbers 11 and 12 in the attachted document.
I'm not trying to cheat because the answers are already given.. It's not marked work..
This is not a tutorial service.
Both of those questions turn on this fact: $\displaystyle \frac{1}{z} = \frac{{\overline z }}{{\left| z \right|^2 }}$.
Example: $\displaystyle \frac{1}{3-4i}=\frac{3+4i}{25}$.
If $\displaystyle (1+3i)z=2+i$ then $\displaystyle z=\frac{(2+1)(1-3i)}{10}$.