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Proving an identity

Please explain how to prove the identity with the following example:
sin x - sin 3x / cos x - cos 3x = -cot 2x

Solution Preview

Use the identities
sinA-sinB=2cos[(A+B)/2]sin[(A-B)/2]
cosA-cosB=2sin[(A+B)/2]sin[(B-A)/2]
Let A=x and B=3x, we have
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Solution Summary

This provides an example of proving a given trigonometric identity.

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