Trigonometric Identities Question 21
Question: The value of $ \cos 52{}^\circ +\cos 68{}^\circ +\cos 172{}^\circ $ is
[MP PET 1997; Pb. CET 1995, 99]
Options:
A) 0
B) 1
C) 2
D) $ \frac{3}{2} $
Show Answer
Answer:
Correct Answer: A
Solution:
$ \cos 52^{o}+\cos 68^{o}+\cos 172^{o} $ $ =(\cos 52^{o}+\cos 172^{o})+\cos 68^{o} $ $ =2\cos 112^{o},\cos 60^{o}+\cos 68^{o} $ $ =\cos 112^{o}+\cos 68^{o}=2\cos (90^{o})\cos 22^{o}=0 $ .
BETA
