Roots of One 
 
       Definition
 The equation
  \[
   x^p = 1
  \]
  has $p$ roots and these are called the $p$
  roots of 1.
 We call the complex numbers which solve this
  equation the $p$th roots of
  one or the ($p$th) roots
  of unity.
 A $n$th root of unity $r \in \R $ is
  primitive if it is not
  an $m$th root of unity for any $m < n$.