# Thread: Need a hand on this problem

1. ## Need a hand on this problem

Hello all,
I am new to this forum as my post counter will show, and I have a toughy right out of the box. Can someone please point me in the right direction?
I am a little fuzzy on this as I have not been in school for 20 years.
Goes to show how much we use this junk huh?

DeMoivre’s Theorem states, “If z = r(cos u + i sin u), then zn = rn(cos nu + i sin nu).”

I have to verify for n=2. Where the heck am I supposed to start?
I do not remember DeMoivre's Theorem.
Any help would be greatly appreciated.

2. $\begin{array}{rcl}
{\left[ {\cos (t) + i\sin (t)} \right]^2 } & = & {\left( {\cos ^2 (t) - \sin ^2 (t)} \right) + i\left( {2\cos (t)\sin (t)} \right)} \\
{} & = & {\cos (2t) + i\sin (2t)} \\

\end{array}$