# Thread: Trig Difference Identity: when I do sin(-15) = sin(30-45), I get a positive result

1. ## Trig Difference Identity: when I do sin(-15) = sin(30-45), I get a positive result

Hello,

I am trying to find sin(-15). Do the difference identities apply to negative angles? I am struggling to come up with the correct answer because when I do sin(-15) = sin(30-45), I get a positive result. Can someone please explain the flaw in my logic?

Thanks!

2. sin(-15) does not equal sin(15), just look at the graph of sin(x).
Edit: please disregard, misunderstood the question. Yes, your approach should work. How did you evaluate sin(30-45)?

3. Originally Posted by BigNate
Hello,

I am trying to find sin(-15). Do the difference identities apply to negative angles? I am struggling to come up with the correct answer because when I do sin(-15) = sin(30-45), I get a positive result. Can someone please explain the flaw in my logic?

Thanks!
It should work for any angle; can you show the details of your work, so we can find the flaw?

My guess is that you either used the wrong formula, or made a little sign error.

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