A) 1/2
B) -1/2
C) 1/4
D) 1
Correct Answer: C
Solution :
\[\sin \frac{\pi }{10}\sin \frac{3\pi }{10}=\sin 18{}^\circ .\sin 54{}^\circ \] \[=\sin 18{}^\circ .\cos 36{}^\circ =\frac{\sqrt{5}-1}{4}.\frac{\sqrt{5}+1}{4}=\frac{1}{4}\].
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