Question 1.29: Find each of the indicated roots and locate them graphically...

Find each of the indicated roots and locate them graphically.

(a) (-1+i)^{1 / 3} , (b) (-2 \sqrt{3}-2 i)^{1 / 4}

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(a) (-1+i)^{1 / 3}

\begin{aligned} -1+i &=\sqrt{2}\{\cos (3 \pi / 4+2 k \pi)+i \sin (3 \pi / 4+2 k \pi)\} \\ (-1+i)^{1 / 3} &=2^{1 / 6}\left\{\cos \left(\frac{3 \pi / 4+2 k \pi}{3}\right)+i \sin \left(\frac{3 \pi / 4+2 k \pi}{3}\right)\right\} \end{aligned}

If k=0, z_1=2^{1 / 6}(\cos \pi / 4+i \sin \pi / 4).
If k=1, z_2=2^{1 / 6}(\cos 11 \pi / 12+i \sin 11 \pi / 12).
If k=2, z_3=2^{1 / 6}(\cos 19 \pi / 12+i \sin 19 \pi / 12).

These are represented graphically in Fig. 1-32.

(b) (-2 \sqrt{3}-2 i)^{1 / 4}

\begin{gathered} -2 \sqrt{3}-2 i=4\{\cos (7 \pi / 6+2 k \pi)+i \sin (7 \pi / 6+2 k \pi)\} \\ (-2 \sqrt{3}-2 i)^{1 / 4}=4^{1 / 4}\left\{\cos \left(\frac{7 \pi / 6+2 k \pi}{4}\right)+i \sin \left(\frac{7 \pi / 6+2 k \pi}{4}\right)\right\} \end{gathered}

If k=0, z_1=\sqrt{2}(\cos 7 \pi / 24+i \sin 7 \pi / 24).
If k=1, z_2=\sqrt{2}(\cos 19 \pi / 24+i \sin 19 \pi / 24).
If k=2, z_3=\sqrt{2}(\cos 31 \pi / 24+i \sin 31 \pi / 24).
If k=3, z_4=\sqrt{2}(\cos 43 \pi / 24+i \sin 43 \pi / 24)

These are represented graphically in Fig. 1-33.

1.32
1.33

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