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Show that CosA=(Cos3A)/(2Cos2A-1). Hence...

Show that `CosA=(Cos3A)/(2Cos2A-1)`. Hence find the value of `Cos15^(@)`

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The correct Answer is:
`(sqrt3+1)/(2sqrt2)`
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AAKASH SERIES-MULTIPLE & SUBMULTIPLE ANGLES-EXERCISE 3.1 ( SHORT ANSWER QUESTION )
  1. If none of 2A, 3A is an odd multiple of pi/2 then prove that tan 3A ...

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  2. For alpha , beta in R, prove that (cos alpha + cos beta )^(2)+ (sin al...

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  3. IF theta is not an integral muliple of pi/2, prove that tantheta+2ta...

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  4. Prove that (cos3A + sin3A)/(cosA - sin A) = 1+ 2sin 2A.

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  5. Prove that cot(pi/4-theta)=(cos2theta)/(1-sin2theta) and hence find th...

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  6. If theta lies in third Quardrant and Sintheta=(-4)/5. Find the values ...

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  7. If 450^(@)lt theta lt 540^(@) and Sintheta=12/13 then calculate "Sin"t...

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  8. Prove that (sin2A)/((1+Cos2A))((CosA))/(1+CosA)=tan.A/2

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  9. (Cos^(3)theta-Cos3theta)/(Costheta)+(Sin^(3)theta+Sin3theta)/(Sintheta...

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  10. Show that CosA=(Cos3A)/(2Cos2A-1). Hence find the value of Cos15^(@)

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  11. Show that sin A= (sin 3A) /(1+2 cos 2A). Hence find the value of sin 1...

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  12. Prove that tanalpha=(Sin2alpha)/(1+cos2alpha) and hence deduce the val...

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  13. In aDelta^("le") ABC If "Tan"(A)/(2)=(5)/(6),"Tan"(B)/(2)=(20)/(37) th...

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  14. If Costheta=5/13 and 270^(@)ltthetalt360^(@). Evaluate "Sin"theta/2 an...

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  15. If 180^(@)lt thetalt270^(@) and Sintheta=(-4)/5 calculate "Sin"theta/2...

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  16. Show that sin""(pi)/5.sin""(2pi)/5.sin""(3pi)/5.sin""(4pi)/5=5/16.

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  17. Prove that cos ^(2). (pi)/(8) + cos ^(2). (3pi)/(8)+ cos ^(2). (5 pi )...

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  18. Prove that "Cos"^(2)(pi/10)+"Cos"^(2)((2pi)/5)+"Cos"^(2)((3pi)/5)+"Cos...

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