A) \[\cos \theta +i\,\sin \theta \]
B) \[\cos \theta -i\,\sin \theta \]
C) \[\cos \theta \pm i\,\sin \theta \]
D) \[\sin \theta \pm i\,\cos \theta \]
Correct Answer: C
Solution :
\[x+\frac{1}{x}=2\cos \theta \]\[\Rightarrow \,{{x}^{2}}-2x\cos \theta +1=0\] Þ \[x=\frac{2\cos \theta \pm \sqrt{4{{\cos }^{2}}\theta -4}}{2}\] Þ \[x=\cos \theta \pm i\sin \theta \].
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