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"cos"^(2)pi/10+"cos"^(2)(2pi)/5+"cos"^(2...

`"cos"^(2)pi/10+"cos"^(2)(2pi)/5+"cos"^(2)(3pi)/5+"cos"^(2)(9pi)/10=`

A

1

B

2

C

4

D

6

Text Solution

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The correct Answer is:
B
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AAKASH SERIES-MULTIPLE & SUBMULTIPLE ANGLES-EXERCISE-II
  1. If 630^@ lt A lt 720^(@) , |tan A|=12//5, " then " tan A//2=

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  2. Prove that (1+cos""pi/10)(1+cos""(3pi)/10)(1+cos""(7pi)/10)(1+cos""(9p...

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  3. "cos"^(2)pi/10+"cos"^(2)(2pi)/5+"cos"^(2)(3pi)/5+"cos"^(2)(9pi)/10=

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  4. Show that cos^4""pi/8+cos^4""(3pi)/8+cos^4""(5pi)/8+cos^4""(7pi)/8=3/2

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  5. tan9^(@)-tan27^(@)-tan63^(@)+tan81^(@)=

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  6. x/(costheta)=y/(cos(theta-(2pi)/3))=z/(cos(theta+(2pi)/3)) then x+y+z=

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  7. The minimum value of cos^(3) x+ cos^(3) (120^(@) + x) + cos^(3) (120^...

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  8. If x= tan15^(@) , y="cosec"75^@ and z= 4 sin18^(@) , then

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  9. cos^(2)(alpha+beta)+cos^(2)(alpha-beta)-cos2alpha cos2beta=

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  10. If cos^(3) theta + cos^(3)((2pi)/(3) + theta) + cos^(3)((4pi)/(3) + th...

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  11. If tan(theta/2)=cosec theta-sintheta then the numerical balue of "cos"...

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  12. If cos theta = (cos alpha - cos beta)/(1-cos alpha cos beta), then one...

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  13. If x+y+z=xyz , " then " sum(3x-x^(3))/(1-3x^(2))=

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  14. tan ""7(1^@)/(2)=

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  15. If sin18^(@)=(sqrt5-1)/4 then Sin81^(@)=

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  16. If sqrt(1+sinA)-sqrt(1-sinA)=2"sin"A/2"then"A/2 in

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  17. If (3pi)/4ltA/2lt(5pi)/4 then -sqrt(1+sinA)+sqrt(1-sinA)=

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  18. I : If (cos alpha )/(a)=(sin alpha )/(b) then a cos 2 alpha + b cos 2...

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  19. If A=6 sin20^(@) - 8 sin^(3) 20^@ , B= 8 cos^(3) 20^(@)-6 cos 20^(@) ...

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  20. Match the following .{:((1) tan(pi/4+theta)-tan(pi/4-theta)=,(a) 1),...

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