As raízes quartas de $1$

Como $z = 1 = \operatorname{cis} \left( 0 \right)$, então as suas raízes quartas são:

$$\begin{array}{*{20}{l}}
{k = 0:}&{{w_0} = \operatorname{cis} \left( {\frac{0}{4}} \right) = \operatorname{cis} \left( 0 \right) = 1} \\
{k = 1:}&{{w_1} = \operatorname{cis} \left( {\frac{0}{4} + \frac{{2\pi }}{4}} \right) = \operatorname{cis} \left( {\frac{\pi }{2}} \right) = i} \\
{k = 2:}&{{w_2} = \operatorname{cis} \left( {\frac{0}{4} + \frac{{4\pi }}{4}} \right) = \operatorname{cis} \left( \pi  \right) =  – 1} \\
{k = 3:}&{{w_3} = \operatorname{cis} \left( {\frac{0}{4} + \frac{{6\pi }}{4}} \right) = \operatorname{cis} \left( {\frac{{3\pi }}{2}} \right) =  – i}
\end{array}$$

As raízes quartas de $z = 1$.