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Math Help - Help checking compound angles question

  1. #1
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    Help checking compound angles question

    Hi
    Forgive me if this is the incorrect forum - I consider compound angles to be trig, but maybe they're not!

    I'm struggling to obtain the same answer as that given in a textbook. I'll give you my answer - I'd appreciate any help where I might have gone wrong:

    Convert -3 \, sin\,\omega t-6 \,cos\,\omega t to the form R\,sin\,(\omega t\pm \alpha)

    I make this 6.708sin(\omega t- 4.2487)

    Is this in the 3rd quadrant as I think it is? The answer the book gives seems to imply the answer is in the second quadrant.
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  2. #2
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    answer correct!
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  3. #3
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    Quote Originally Posted by mestmoha View Post
    answer correct!
    I think I figured out why they differ. For it to be in the 3rd quadrant, I assume the angle has to be *less* than pi, else it will fall in the 1st or 2nd quadrant (as it is a negative angle, and we're working back from zero).

    I'm starting to think the book is right
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