[m]z=r\cdot (cos \phi+i\cdot sin\phi)[/m] ⇒ [m]z^{n}=r^{n}\cdot (cos (n\cdot \phi)+i\cdot sin (n\cdot \phi))[/m]
[m]z_{1}=14\cdot (cos\frac{5\pi}{27}+i\cdot sin\frac{5\pi}{27})[/m]
[m]z^{2}_{1}=14^{2}\cdot (cos(2\cdot \frac{5\pi}{27})+i\cdot sin(2\cdot \frac{5\pi}{27}))[/m]
[m]z^{2}_{1}=196 \cdot (cos \frac{10\pi}{27}+i\cdot sin \frac{10\pi}{27})[/m]