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Prove that cos (pi + theta) = - cos th...

Prove that
` cos (pi + theta) = - cos theta`

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The correct Answer is:
`- cos theta`
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SURA PUBLICATION-TRIGONOMETRY-EXERCISE 3.4
  1. Find the value of tan (7pi)/(12)

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  2. Prove that cos (30^(@) + x) = (sqrt(3) cos x - sin x)/(2)

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  3. Prove that cos (pi + theta) = - cos theta

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  4. Prove that sin (pi + theta) = - sin theta

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  5. Find a quadratic equation whose roots are sin 15^(@) and cos 15^(@)

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  6. Expand cos ( A + B + C). Hence prove that cos A cos B cos C = sin A si...

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  7. Prove that sin (45^(@) + theta) - sin (45^(@) - theta) = sqrt(2) sin...

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  8. Prove that sin (30^(@) + theta) + cos (60^(@) + theta) = cos theta

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  9. If a cos (x + y) = b cos (x - y), show that (a + b)tan x = (a - b) cot...

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  10. Prove that sin 105^(@) + cos 105^(@) = cos 45^(@)

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  11. Prove that sin 75^(@) - sin 15^(@) = cos 105^(@) + cos 15^(@)

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  12. Show that tan 75^(@) + cot 75^(@) = 4

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  13. Prove that cos (A + B) cos C - cos (B + C) cos A = sin B sin (C - A)

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  14. Prove that sin (n + 1)theta sin (n - 1) theta + cos (n + 1)theta cos (...

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  15. If x cos theta = y cos (theta + (2pi)/(3))= z cos (theta + (4pi)/(3)) ...

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  16. Prove that sin ( A + B) sin (A - B) = sin^(2) A - sin^(2)B.

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  17. Prove that cos (A + B) cos (A - B) = cos^(2) A - sin^(2) B = cos^(2) ...

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  18. Prove that sin^(2)(A + B) - sin^(2)(A - B) = sin 2A sin 2B

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  19. Prove that cos 8theta cos 2theta = cos^(2) 5theta- sin^(2) 3 theta

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  20. Show that cos^(2) A + cos^(2)B - 2 cos A cos B cos (A + B) = sin^(2) (...

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