Trigonometric Identities Question 54
Question: $ \cos 20{}^\circ \cos 40{}^\circ \cos 80{}^\circ = $
[MP PET 1989]
Options:
A) 1/2
B) 1/4
C) 1/6
D) 1/8
Show Answer
Answer:
Correct Answer: D
Solution:
$ \cos 20^{o}\cos 40^{o}\cos 80^{o}=\frac{\sin 2^{3}20^{o}}{2^{3}\sin 20^{o}} $ $ =\frac{\sin 160^{o}}{8\sin 20^{o}}=\frac{1}{8} $ .