The centre of a regular polygon of $n$ sides is located at the point $z = 0$ and one of its vertices $z_1$ is known. If $z_2$ is the vertex adjacent to $z_1$,then $z_2$ is equal to

• A
  $z_1 \left( \cos \frac{2\pi}{n} \pm i \sin \frac{2\pi}{n} \right)$
• B
  $z_1 \left( \cos \frac{\pi}{n} \pm i \sin \frac{\pi}{n} \right)$
• C
  $z_1 \left( \cos \frac{\pi}{2n} \pm i \sin \frac{\pi}{2n} \right)$
• D
  None of these