Can some one explain to me what is going on here - power of complex number

So here is the question and the work to solve it, but I have no idea how one knows to do the first step or what the first step is...

$$ \begin{align}
(6-i\sqrt{12})^{12} &= \left[\sqrt{48}\left(\cos\left(\frac{\pi}{6}\right) - i\sin\left(\frac{\pi}{6}\right)\right)\right]^{12}\\

&= (\sqrt{48})^{12} \left[\cos\left(\frac{12\pi}{6}\right) - i\sin\left(\frac{12\pi}{6}\right)\right]\\
&=48^6
\end{align}
$$

Answer

Step 1 Write your number in polar coordinates, i.e. $z=r(\cos t+i\sin t)$.

Step 2 Use De Moivre's theorem, that $(\cos t+i\sin t)^n=\cos nt+i\sin nt$.