Trig

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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  1. Identities are trigonometric equations that must be valid for any value of the angle. That is only true for the first equation.

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