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cos""(2pi)/(15)cos""(4pi)/(15)cos""(8pi)...

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

A

0

B

1

C

`-1`

D

`1//8`

Text Solution

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The correct Answer is:
D
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OBJECTIVE RD SHARMA ENGLISH-TRIGONOMETRIC RATIOS AND IDENTITIES-Exercise
  1. The value of sin""(pi)/(7)+sin""(2pi)/(7)+sin""(3pi)/(7), is

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

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

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

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

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

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

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  8. If n=pi/(4alpha), then tan alpha tan 2alpha tan 3 alpha ... tan(2n-1)a...

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  9. The value of tan9^@-tan2 7^@-tan6 3^@+tan8 1^@ is equal to

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  10. For x in R, tanx+1/2tan""(x)/(2)+1/((2^2))tan""(x)/(2^(2))+...+(1)/(...

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  11. If (tan3A)/(tanA)=k, then (sin3A)/(sinA)=

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  12. If y=(sec^(2)theta-tantheta)/(sec^(2)theta+tantheta)'then

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  13. If cosA=tanB, cos B=tanC, cosC=tanA, then sin A is equal to

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  14. If tanalpha is equal to the integral solution of the inequality 4x^2-1...

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  15. If x/(costheta)=y/(cos(theta-(2pi)/3))=z/(cos(theta+(2pi)/3)) 1 (b) ...

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  16. If cosA=3/4, then 32 sin (A/2) sin ((5A) /2)= ------------- ...

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  17. Find the minimum value of 9tan^2theta+4cot^2theta

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  18. If x(1),x(2),x(3),...,x(n) are in A.P. whose common difference is alph...

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  19. If asin^2x+bcos^2x=c,bsin^2y+acos^2y=d and atanx=btany then a^2/b^2=.....

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  20. If a(r+1)=sqrt(1/2 ( 1+a(r))), the prove that cos((sqrt(1-a(0)^(2))...

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