de Moivre's question

The other evening I was doing some reading when I received a sms from an ex-student, asking me about solving this question using de Moivre's theorem. To provide some background, I taught this student O-Level physics and he has since moved on to study engineering in polytechnic. As for de Moivre's theorem, did I only learn it in university?

I clarified with him a bit on the question (those brackets and powers are confusing on sms), and proposed to discuss it on facebook. He replied that he was outside and asked me to call him. Free incoming calls, I have that too. So I was preparing to sms him the answer when he finally couldn't take the wait and called me up. Had I still be a teacher with more energy and time, I would have taught those kids what it means to ask someone for a favour, but not making things easier for them to help you. (just like the previous instance. In fact the same student was involved)

Anyway, we both couldn't get the "textbook" answer. Must be printing error, hur hur.

The ex-student went on to ask if I could give him tuition on engineering topics such as Kirchhoff’s current law and all sorts of circuitry stuff. I told him that nowadays I myself is studying, so I wouldn't have the time (and energy) to teach him. His reply was "wah you hardcore leh!"

One line in the Teacher's Pledge says "We will continue to learn and pass on the love of learning to our pupils". I hope that is the minimum I could pass on.