Trigonometric Identities Question 330
Question: $ 2{{\cos }^{2}}\theta -2{{\sin }^{2}}\theta =1 $ ,then $ \theta $ =
[Karnataka CET 1998]
Options:
A) $ 15{}^\circ $
B) $ 30{}^\circ $
C) $ 45{}^\circ $
D) $ 60{}^\circ $
Show Answer
Answer:
Correct Answer: B
Solution:
$ 2{{\cos }^{2}}\theta -2{{\sin }^{2}}\theta =1 $
Þ $ 2\cos 2\theta =1 $
Þ $ \cos 2\theta =\frac{1}{2}=\cos 60^{o} $
Þ $ 2\theta =60^{o}\Rightarrow \theta =30^{o} $ .
BETA
