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Math Help - Trigonometry

  1. #1
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    Trigonometry

    Given that sin20 = k, express tan(-20) in terms of k.
    I do not really understand this chapter and I was stumped at this question.
    Any help and explanation would be greatly appreciated because my teacher has been changed to a trainee from the education institute and I don't get what she's saying half the time.
    Thank you very much in advance!
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  2. #2
    MHF Contributor Amer's Avatar
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    \sin 20 = k

    use the identity \sin ^2 x + \cos ^2 x = 1

    \cos 20^o = \sqrt{1 - k^2 }

    so \tan 20^o = \frac{\sin 20^o }{\cos 20^o }

    \tan 20^o = \frac{k}{\sqrt{1- k^2}}
    Last edited by Amer; August 9th 2010 at 05:53 AM.
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  3. #3
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    Notice that the problem is not yet finished, caramelcake. You asked for tan(-20) and Amer gave you tan(20). Of course, it is easy to finish now.
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  4. #4
    Senior Member eumyang's Avatar
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    Sorry to nitpick, Amer, but you forgot the degree signs. If I see this:
    \sin 20
    I'm going to assume that you mean 20 radians, not 20 degrees.

    This is a pet peeve of mine. I see kids doing this all the time, and it drives me nuts.
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  5. #5
    MHF Contributor Amer's Avatar
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    Quote Originally Posted by eumyang View Post
    Sorry to nitpick, Amer, but you forgot the degree signs. If I see this:
    \sin 20
    I'm going to assume that you mean 20 radians, not 20 degrees.

    This is a pet peeve of mine. I see kids doing this all the time, and it drives me nuts.
    what about now is it ok
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  6. #6
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    You should have posted this in the trigonometry section where others may benefit.
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