A) \[2\cos \theta \]
B) \[2\sin \theta \]
C) \[2\text{cosec}\theta \]
D) \[2\tan \theta \]
Correct Answer: A
Solution :
\[y=\cos \theta +i\sin \theta ={{e}^{i\theta }},\] then \[\frac{1}{y}={{e}^{-i\theta }}=\cos \theta -i\sin \theta \] \[\therefore y+\frac{1}{y}=2\cos \theta \].
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