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If B + C = 60^@, show that : sin (120^@...

If `B + C = 60^@`, show that :
`sin (120^@- B) = sin (120^@ -C) `.

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MODERN PUBLICATION-TRIGNOMETRY-EXERCISE
  1. If x=(11 pi)/4, prove that : sin^2 x- cos^2 x+2 tan x- sec^2 x=1.

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  2. If 8 theta=pi, prove that cos theta+ cos 7 theta=0.

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  3. If B + C = 60^@, show that : sin (120^@- B) = sin (120^@ -C) .

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  4. Prove that : sin^2 frac (pi)(8)+ sin^2 frac (3pi)(8)+ sin^2 frac (5pi)...

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  5. Prove that : [1+ cot alpha- sec (pi/2+alpha)] [1+ cot alpha+ sec (pi/...

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  6. In any triangle ABC, prove that : sin (A + B) = sin C.

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  7. In any triangle ABC, prove that : cos frac (A+B)(2)= sin frac (C)(2).

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  8. In any triangle ABC, prove that : tan frac (B+C-A)(2)= cot A.

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  9. If cot A= tan (n-1) A, show that one value of A is pi/(2n).

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  10. Show that the function f(x) = cos 2x is periodic and find its period.

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  11. Show that the function f(x) = cos (x/2+pi/4) is periodic and find its ...

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  12. Evaluate : sin 15^@, cos 15^@, tan 15^@.

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  13. Evaluate : sin 75^@, cos 75^@, tan 75^@.

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  14. Prove that : sin 105^@ + cos 105^@=1/sqrt2.

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  15. Prove that : cos 105^@ + cos 15^@= sin 75^@- sin 15^@ .

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  16. Find tan 15^@ and hence show that tan 15^@+ cot 15^@ = 4.

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  17. Evaluate : sin^2 (15^@ + A) - sin^2 (15^@ -A).

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  18. Write down the values of : cos 68^@ cos 8^@ + sin 68^@ sin 8^@.

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  19. Write down the values of : cos 70^@ cos 10^@ + sin 70^@ sin 10^@.

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  20. Prove that : cos 130^@ cos 40^@+ sin 130^@ sin 40^@= 0.

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