Complex Numbers And Quadratic Equations question 832
Question: If $ y=\cos \theta +i\sin \theta $ ,then the value of $ y+\frac{1}{y} $ is [RPET 1995]
Options:
A) $ 2\cos \theta $
B) $ 2\sin \theta $
C) $ 2cosec\theta $
D) $ 2\tan \theta $
Show Answer
Answer:
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 $ .
BETA
