(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I should know this, but I'm using it as a step in one of my proofs and having trouble explaining how it works. Can someone help?

-sin^{2}x - cos^{2}x = -1

2. Relevant equations

3. The attempt at a solution

Not sure how to prove and explain it.

And sorry about the title gents I'm using a blackberry so I just copied and pasted the equation from my question : /

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# Homework Help: Explain why -sin[SUP]2[/SUP]x - cos[SUP]2[SUP]x = -1

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