The value of $c o s 10^{0} . c o s 20^{0} . c o s 30^{0} . . . . . . . . c o s 80^{0} . . . . . . . c o s 900^{0} . . . . . c o s 1790^{0}$ is ?

\frac{1}{\sqrt{2}}

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0

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1

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N o n e o f t h e s e

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Solution

The correct option is B $0$
$c o s 10^{0} . c o s 20^{0} . c o s 30^{0} . . . . . . . . c o s 80^{0} . . . . . . . c o s 900^{0} . . . . . c o s 1790^{0}$

We know $c o s 90^{0} = 0$

So the product is

$c o s 10^{0} . c o s 20^{0} . c o s 30^{0} . . . . . . . c o s 80^{0} . . . . . . . c o s 90^{0} . . . . . c o s 1790^{0}$

=0

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Similar questions

cos 20^{\circ} cos 100^{\circ} + cos 100^{\circ} cos 140^{\circ} - cos 140^{\circ} cos 200^{\circ}

{[\frac{cos 10^{0} + sin 20^{0}}{cos 20^{0} - sin 10^{0}}]}^{2}

cos 20^{\circ} cos 100^{\circ} + cos 100^{\circ} cos 140^{\circ} - cos 140^{\circ} cos 200^{\circ}

cos 20^{\circ} cos 100^{\circ} + cos 100^{\circ} cos 140^{\circ} - cos 140^{\circ} . cos 200^{\circ}

	List I		List II
A.	$cos 20^{\circ} + cos 80^{\circ} - \sqrt{3} cos 50^{\circ}$	1.	$- 1$
B.	$cos 0^{\circ} + cos \frac{π}{7} + cos \frac{2 π}{7} + cos \frac{3 π}{7} + cos \frac{4 π}{7} + cos \frac{5 π}{7} + cos \frac{6 π}{7}$	2.	$- \frac{3}{4}$
C.	$cos 20^{\circ} + cos 40^{\circ} + cos 60^{\circ} + 4 cos 10^{\circ} cos 20^{\circ} cos 30^{\circ}$	3.	$1$
D.	$cos 20^{\circ} cos 100^{\circ} + cos 100^{\circ} cos 140^{\circ} - cos 140^{\circ} cos 200^{\circ}$	4.	$0$

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