Solutions to $z^3 - z^2- z =15 $ Find in the form $a+bi$, all the solutions to the equation
$$z^3 - z^2- z =15 $$
I have no idea what to do - am I meant to factor out z to get $z(z^2-z-1)=15$ or should I plug in $a+bi$ to z? 
Please help!!!!!!!  

Hint: First find the one real root, say $r$ (it's not hard). Then you can factor out $z-r$ out of $z^3-z^2-z-15=0$, and find the remaining roots using the quadratic formula.
