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Find the value of cos(2pi)/7+cos(4pi)/7+...

Find the value of `cos(2pi)/7+cos(4pi)/7+cos(6pi)/7`

A

1

B

`-1`

C

`1//2`

D

`-1//2`

Text Solution

Verified by Experts

The correct Answer is:
D
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OBJECTIVE RD SHARMA ENGLISH-TRIGONOMETRIC RATIOS AND IDENTITIES-Exercise
  1. The value of cot36^(@)cot72^(@), is

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  2. The value of cospi/7+cos(2pi)/7+cos(3pi)/7+cos(4pi)/7+cos(5pi)/7+cos(6...

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  3. Find the value of cos(2pi)/7+cos(4pi)/7+cos(6pi)/7

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  4. The value of cos""(pi)/(9)cos""(2pi)/(9)cos""(3pi)/(9), is

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  5. Prove that cos ""(pi)/(9) cos ""( 2pi)/(9) cos "" (3pi)/(9) cos ""(4pi...

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  6. The vlaue of cosec^(2)""(pi)/(7)+cosec^(2)""(2pi)/(7)+cosec^(2)""(3pi)...

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  7. sin1 2^(@)sin4 8^(@)sin5 4^(@)=

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  8. the value of sin(pi/7)+sin((2pi)/7)+sin((3pi)/7) is

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  9. tan^6pi/9-33tan^4pi/9+27tan^2pi/9 is equal to (a) 0 (b) sqrt(3) (c)...

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  10. (sin^2 3A)/(sin^2A)-(cos^2 3A)/(cos^2A)=

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  11. If sinA=(336)/(625)where450^(@)ltAlt540^(@), then sin""(A)/(4)=

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  12. If y=(tanx)/(tan3x), then

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  13. The value of cot^(2)""(pi)/(7)+cot^(2)""(2pi)/(7)+cot^(2)""(3pi)/(7), ...

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  14. The value of sin""(pi)/(7)+sin""(2pi)/(7)+sin""(3pi)/(7), is

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  15. Prove that sin. (2pi)/(7)+sin.(4pi)/(7)+sin. (8pi)/(7)=(sqrt(7))/(2).

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  16. cos""(2pi)/(15)cos""(4pi)/(15)cos""(8pi)/(15)cos""(16pi)/(15)=(1)/(16)

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  17. If sinA+cosA=m an sin^(3)A+cos^(3)A=n, then

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  18. If cosA+cosB=m and sinA+sinB=n then sin(A+B)=

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  19. If 0ltA lt(pi)/(6) and sinA+cosA=(sqrt7)/(2),"then" tan""(A)/(2)=

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  20. Find the value of cos""(pi)/(11)+cos""(3pi)/(11)+cos""(5pi)/(11)+cos""...

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