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Problems on trigonometric identities and equations

Prove this identity:

7. sin(x+y)/sin(x-y) = coty +cotx / coty - cot x

8. simplify:
2 sinxcos³x - 2 sin³xcosx

9. If cosx=-1/4 and pie/2<x<pie, the cos (pie/6 - x) = ?

10. Prove this identity:
cos 8x = cos²4x - sin²4x

Solution Summary

Methods to simplify trigonometric expressions using simple and fundamental trigonometric identities are discussed.

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