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if ( cos ^(3) 20^@ + cos^(3) 40^(@))/( c...

if `( cos ^(3) 20^@ + cos^(3) 40^(@))/( cos 20^@+ cos 40^(@)) = k ` ,then the value of k is

A

`4//3`

B

`3//4`

C

`3//2`

D

`2//3 `

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The correct Answer is:
B
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  2. 4( cos^(3) 10^(@) + sin^(3) 20^(@))=

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  3. if ( cos ^(3) 20^@ + cos^(3) 40^(@))/( cos 20^@+ cos 40^(@)) = k ,the...

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  4. cos theta cos (60^(@) + theta ) * cos (60^(@) - theta ) =

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  5. sin^(2) theta + sin^(2)(60^@ + theta ) + sin^(2)(60^(@) - theta ) =

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  6. cos^(2) A + cos^(2) ( 120^(@) + A)+ cos^(2) (120^(@) - A )=

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  7. cos^(3) theta + cos^(3) ( 120^(@) +theta ) + cos^(3) (120^(@) - theta ...

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  8. sin^(2) 20^(@) + sin^(2) 100^@ + sin^(2) 140^(@) =

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  9. cos^(3) 20^(@) + cos^(3) 100^(@) + cos^(3) 140^(@) =

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  10. cos^(2)(theta-45^(@))+cos^(2)(theta+15^(@)-cos^(2)(theta-15^(@))=

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  11. If 4 sin(60^(@) + theta ) sin (60^(@) - theta )-1=k cos 2 theta , th...

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