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Prove that : cos^2 A+cos^2 (A+120^@)+ ...

Prove that :
`cos^2 A+cos^2 (A+120^@)+ cos^2 (A-120^@)=3/2`.

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MODERN PUBLICATION-TRIGNOMETRY-EXERCISE
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  2. Prove that sin frac (pi)(14) sin frac (3 pi)(14) sin frac (5pi)(14) si...

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  3. Prove that : cos^2 A+cos^2 (A+120^@)+ cos^2 (A-120^@)=3/2.

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  6. If alpha and beta are two real numbers satisfying the equation a cos x...

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  7. If alpha and beta are two real numbers satisfying the equation a cos x...

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  8. If (sin^4 theta)/a+ (cos^4 theta)/b= 1/(a+b), prove that (sin^12 thet...

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  9. If (sin^4 theta)/a+ (cos^4 theta)/b= 1/(a+b), prove that (sin^(4n) th...

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  10. If a tan alpha+b tan beta=(a+b) tan ((alpha+beta)/2), where alpha ne b...

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  11. If alpha and beta are the solution of a cos theta + b sin theta = c...

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  12. If alpha and beta are the solutions of a cos theta+b sin theta=c, the...

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  13. If alpha and beta are distinct roots of the equation : a tan theta+b s...

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  14. Prove that cot 7 1^@/2 = (1+cos15^@)/(sin 15^@).

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  15. Prove that 4 cos 36^@ +cot 7 1^@/2 = sqrt1+sqrt2 +sqrt3+ sqrt4+ sqrt5+...

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  16. Prove that tan 82 (1(0))/(2)=(sqrt(3)+sqrt(2))(sqrt(2)+1) or cot 7 (...

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  17. Prove that 4 sin 27^@ = sqrt(5+sqrt5)+sqrt(3-sqrt5).

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  18. If tan beta= (Q sin alpha)/(P+Q cos alpha), prove that : tan (alpha-b...

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  19. Prove that cot theta cot 2 theta+ cot 2 theta cot 3 theta+ 2= cot thet...

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  20. Prove that: (cos 2A cos 3A-cos 2A cos 7A + cos A cos 10A)/(sin 4A sin ...

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