# Homework Help: U4 set

1. Jul 4, 2006

### Taviii

I saw this problem in a book: calculate the sum of the elements of the U4 set.

The answer is 0, the elements of the sets being: 1, i, -1, -i.

My questions is: whats the U set?

Last edited: Jul 4, 2006
2. Jul 4, 2006

### maverick280857

In this terminology $U_{n}$ refers to the set of the n-th roots of unity, i.e. all roots of the equation

$$x^{n} - 1 = 0$$

So

$U_{3}$ = {1, $\omega$,$\omega^2$}

3. Jul 5, 2006

Thank you!