# Math Help - De'Moivre's theorem in polar form. Stuck

1. ## De'Moivre's theorem in polar form. Stuck

"Use De Moivre's theorem to solve the following equation, in polar form."

$z^{3}=i$

My working out:
Magnitude:
$z=1$
Angle?
$tan(\theta)=0$
I'm not sure what to do because it's 0 isn't it?

2. Angle is $\displaystyle\frac{\pi}{2}$

$(\cos{\frac{\pi}{2}+i\sin{\frac{\pi}{2})^3$

3. $z^{3}=cis(\frac{\pi}{2})$
$z=cis(\frac{\pi}{2} \times \frac{1}{3} )$
$z=cis(\frac{\pi}{6})$
Ah, I see. Thanks.

5. $\displaystyle e^{i (\frac{\pi}{6} + \frac{2 \pi}{3} n)}$ for n = 0,1,2.

6. Originally Posted by Cthul
$z^{3}=cis(\frac{\pi}{2})$
$z=cis(\frac{\pi}{2} \times \frac{1}{3} )$
$z=cis(\frac{\pi}{6})$
Ah, I see. Thanks.
You have to remember that there are 3 cube roots, and they are evenly spaced around a circle. So they are separated by an angle of $\displaystyle \frac{2\pi}{3}$.

What do you think the other roots are?