Arg, this mark scheme is...rubbish...

Okey, use the fact the suare root of 16 + 30i is (-5 - 3i) and (5 + 3i)

To work out $\displaystyle z^2 - 2z - (15 + 30i)$

Using the formula i got to this stage and got stuck =(

$\displaystyle 2 + or - \frac{\sqrt{64 + 120i}}{2}$

Now i notice if you \ the fraction by 4 you get 16 + 30i which your meant to use...but you can't just do that so uh..wt..

Any help, i'd appreciate loads! Thanks (answer is 6 + 3i and -4 - 3i)

tytyty