Trigonometric Identities Question 296
Question: $ \sin ( \frac{\pi }{10} )\sin ( \frac{3\pi }{10} )= $
[MNR 1984]
Options:
A) 1/2
B) -1/2
C) 1/4
D) 1
Show Answer
Answer:
Correct Answer: C
Solution:
$ \sin \frac{\pi }{10}\sin \frac{3\pi }{10}=\sin 18{}^\circ .\sin 54{}^\circ $ $ =\sin 18{}^\circ .\cos 36{}^\circ =\frac{\sqrt{5}-1}{4}.\frac{\sqrt{5}+1}{4}=\frac{1}{4} $ .
BETA
