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If A+B+C=pi prove that cos^(2) A+cos^(2)...

If `A+B+C=pi` prove that `cos^(2) A+cos^(2) B+cos^(2) C=1 - 2cos A cos B cos C`.

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The correct Answer is:
`1-2 cos A cos B cos C`
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FULL MARKS-TRIGONOMETRY-Exercise 3.12
  1. If A+B+C=pi prove that cos^(2) A+cos^(2) B+cos^(2) C=1 - 2cos A cos B ...

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  2. (1)/(cos 80^(@)) - (sqrt(3))/(sin 80^(@)) =

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  3. If cos 28^(@) + sin 28^(@) = k^(3), then cos 17^(@) is equal to

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  4. The maximum value of 4 sin^(2) x + 3 cos^(2) x + sin ""(x)/(2) + cos""...

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  5. (1 + cos"" (pi)/(8))(1 + cos"" (3pi)/(8)) (1 + cos"" (5pi)/(8))(1 + co...

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  6. If pi lt 2 theta lt (3pi)/(2), then sqrt(2 + sqrt( 2 + 2 cos 4 theta))...

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  7. If tan 40^(@) = lambda, then (tan 140^(@) - tan 130^(@))/(1 + tan 140^...

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  8. cos 1^(@) + cos 2^(@) + cos 3^(@) + ….+ cos 179^(@) =

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  9. Letf(4)(x) = (1)/(k) [ sin^(k) + cos^(k) x ] where x in RR and k ge1. ...

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  10. Which of the following is not true?

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  11. cos 2theta cos 2phi + sin^(2) (theta - phi ) - sin^(2) ( theta + phi) ...

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  12. (sin(A - B))/(cos A cos B) + (sin (B - C))/( cos B cos C) + (sin(C - A...

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  13. If cos ptheta + cos qtheta = 0 and if p ne q, then theta is equal to (...

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  14. If tan alpha and tan beta are the roots of x^(2) + ax + b = 0, then (s...

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  15. In a triangle ABC, sin^(2)A + sin^(2)B + sin^(2)C = 2, then the triang...

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  16. If f(theta) = |sin theta| + |cos theta|,theta in RR, then f(theta) is ...

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  17. (cos 6x + 6 cos 4x + 15 cos 2x + 10)/(cos 5x + 5 cos 3x + 10 cos x ) i...

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  18. The triangle of maximum area with constant perimeter 12m

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  19. A wheel is spinning at 2 radians/second. How many seconds will it take...

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  20. If sin alpha + cos alpha = b, then sin 2alpha is equal to

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  21. In a DeltaABC, if (i)sin (A)/(2) sin"" (B)/(2) sin"" (C )/(2) gt 0 (...

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