( 10 ) ( 3 10 ) = - Vidyadip

MCQ

$\sin \left( {\frac{\pi }{{10}}} \right)\sin \left( {\frac{{3\pi }}{{10}}} \right) = $

A
$1/2$
B
$-1/2$
✓
$1/4$
D
$1$

✓

Answer

Correct option: C.

$1/4$

c
(c) $\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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