# Problems on trigonometric identities and equations

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Prove this identity:

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

8. simplify:

2 sinxcosÂ³x - 2 sinÂ³xcosx

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

10. Prove this identity:

cos 8x = cosÂ²4x - sinÂ²4x.

https://brainmass.com/math/trigonometry/problems-trigonometric-identities-equations-65334

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

We start from right hand side:

We have

. Hence proved.

8. Simplify: 2 sinxcosÂ³x - 2 ...

#### Solution Summary

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

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