Trying to solve this, not allowed to use polar form or Eulers.

Here is my work:

then I have to take the root of

and that didnīt work very well.

Why? What's the problem? You'll have to do the same if you use the well-known formula for the roots of a quadratic equation: you need the square root of , so you can put: , , so are the solutions. Tonio
I tried this too:

rewritting

and

but then it is a

equationsystem with two unknows and one x^3 term etc so that didnīt work either.

and here I am, any ideas?