Find all the complex roots. Write the answer in the indicated form. The complex cube roots of 27(cos 234° + i sin 234°) (polar form)a. 3(cos 78° + i sin 78°), 3(cos198° + i sin 198°), 3(cos 318° + i sin 318°)b. 3(cos 78° + i sin 78°), 3(cos 118° + i sin 118°), 3(cos 158° + i sin 158°)c. -3(cos 78° + i sin 78°), 3(cos 118° + i sin 118°), -3(cos 158° + i sin 158°)d. -3(cos 78° + i sin 78°), 3(cos 198° + i sin 198°), -3(cos 318° + i sin 318°)
Question
Answer:
[tex]\bf \textit{ roots of complex numbers, DeMoivre's theorem}
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\sqrt[n]{z}=\sqrt[n]{r}\left[ cos\left( \cfrac{\theta+2\pi k}{n} \right) +i\ sin\left( \cfrac{\theta+2\pi k}{n} \right)\right]\quad
\begin{array}{llll}
k\ roots\\
0,1,2,3,...
\end{array}\\\\
-------------------------------[/tex][tex]\bf z=27[cos(234^o)+i~sin(234^o)] \\\\\\ \sqrt[3]{z}\implies \sqrt[3]{27}\left[ cos\left( \cfrac{234^o+360^o(0)}{3} \right) +i\ sin\left( \cfrac{234^o+360^o(0)}{3} \right)\right] \\\\\\ 3\left[ cos\left( \cfrac{234^o}{3} \right) +i\ sin\left( \cfrac{234^o}{3} \right)\right]\implies \stackrel{k=0~~1st~root}{3[cos(78^o)+i~sin(78^o)]}\\\\ -------------------------------[/tex]
[tex]\bf \sqrt[3]{z}\implies \sqrt[3]{27}\left[ cos\left( \cfrac{234^o+360^o(1)}{3} \right) +i\ sin\left( \cfrac{234^o+360^o(1)}{3} \right)\right] \\\\\\ 3\left[ cos\left( \cfrac{594^o}{3} \right) +i\ sin\left( \cfrac{594^o}{3} \right)\right]\implies \stackrel{k=1~~2nd~root}{3[cos(198^o)+i~sin(198^o)]}\\\\ -------------------------------[/tex]
[tex]\bf \sqrt[3]{z}\implies \sqrt[3]{27}\left[ cos\left( \cfrac{234^o+360^o(2)}{3} \right) +i\ sin\left( \cfrac{234^o+360^o(2)}{3} \right)\right] \\\\\\ 3\left[ cos\left( \cfrac{954^o}{3} \right) +i\ sin\left( \cfrac{954^o}{3} \right)\right]\implies \stackrel{k=2~~3rd~root}{3[cos(318^o)+i~sin(318^o)]}[/tex]
solved
general
11 months ago
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