Trigonometric Identities Question 327
Question: $ \cos 15{}^\circ = $
[MP PET 1988; MNR 1978]
Options:
A) $ \sqrt{\frac{1+\cos 30{}^\circ }{2}} $
B) $ \sqrt{\frac{1-\cos 30{}^\circ }{2}} $
C) $ \pm \sqrt{\frac{1+\cos 30{}^\circ }{2}} $
D) $ \pm \sqrt{\frac{1-\cos 30{}^\circ }{2}} $
Show Answer
Answer:
Correct Answer: A
Solution:
$ \cos 15^{o}=\sqrt{\frac{1+\cos (2\times 15^{o})}{2}}=\sqrt{\frac{1+\cos 30^{o}}{2}} $ $ ( \because \cos 15^{o}>0 ) $ .
BETA
