Posted by **Melody** on Sunday, January 3, 2010 at 4:07pm.

Are any of these three problems identities?

1. Cos^2x-sin^2x=1-2sin^2x

2. Sinxsecx=cosxcscx

3. Sec^4x-tan^4/sec^2x=1+sin^2x

If so, how can you conclude that any of them are identities?

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