CAn anyone help? I can get to the point where de moivres theorem comes in but I dont understand how to do this...

So the question is;

Express

in the form

and then express

in the form a + ib

SO i can do this part

SO BY DE MOIVRES THEOREM

This is where I can get up to, but what needs to happen here??

in my notes this happens..but I dont undertand it...

Then you plug into the formula r(cos(theta)+isin(theta)