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If tan^2 theta=2 tan^2 phi+1, then which...

If `tan^2 theta=2 tan^2 phi+1`, then which of the following is correct ?

A

`cos (2 theta) = cos (2 phi) - 1`

B

`cos (2 theta) = cos (2 phi)+1`

C

`cos (2 theta) = [cos (2 phi)+1]//2`

D

`cos (2 theta) = [cos (2 phi)-1]//2`.

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MODERN PUBLICATION-TRIGNOMETRY-EXERCISE
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  2. For which acute angle theta cosec^2 theta= 3 sqrt3 cot theta-5?

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  3. If tan^2 theta=2 tan^2 phi+1, then which of the following is correct ?

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  4. The value of sin 10^(@) sin 50^(@) sin 70^(@) is equal to

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  5. The sines of two angles of a triangle are equal to 5/13 and 99/101 . W...

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  6. After subtending an angle of 1000^@ from its initial position, the rev...

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  7. One radian is approximately equal to which one of the following :

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  8. If cot (x+y)= 1/sqrt3, cot (x-y)= sqrt3, then what are the smallest po...

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  9. In sinA= 1/sqrt5, cosB= 3/sqrt10, A, B being positive acute angles, th...

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  10. x = sin theta cos theta, and y = sin theta +cos theta are satisfied by...

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  11. A man observes the elevation of a balloon to be 30^@. He then walks 1 ...

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  12. The number of integral values of k for which the equation 7 cos x + 5 ...

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  13. In a triangle ABC, 2ca sin frac(A-B+C)(2)=

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  14. The period of sin^2 theta is :

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  15. If y = sec^2 theta+ cos^2 theta, theta ne 0, then :

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  16. If alpha is a root of 25 cos^2 theta+ 5 cos theta- 12 = 0,pi/2 < alpha...

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  17. If sin (alpha+beta)=1, sin (alpha-beta)=1/2, then tan (alpha+ 2beta). ...

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  18. In a triangle ABC, tan frac (A)(2)=5/6, tan frac (C)(2)=2/5, then :

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  19. The equation a sin x + b cos x = c, where |c| > sqrt (a^2 +b^2) has :

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  20. In a triangle ABC, a = 4, b=3, angle A = 60^@, then c is the root of t...

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