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Math Help - Trig Identity Problem

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    Trig Identity Problem

    Assuming that is in interval evaluate
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    A Plied Mathematician
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    Re: Trig Identity Problem

    Your pictures are all broken for me. Please post in plain text, or better yet, use LaTeX.
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    Re: Trig Identity Problem

    U is on interval (-pi/2, 0), tan(u)=-1/3 Evaluate sin(2u)
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    Re: Trig Identity Problem

    Quote Originally Posted by bseymore View Post
    U is on interval (-pi/2, 0), tan(u)=-1/3 Evaluate sin(2u)
    sin\ 2u=\frac{2tan\ u}{1+tan^2\ u}
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  5. #5
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    Re: Trig Identity Problem

    sin(2u) = 2sin(u)cos(u)

    sketch a reference triangle in quad IV ... opposite side = -1 , adjacent side = 3

    calculate the hypotenuse and determine the values of sin(u) and cos(u)
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    Re: Trig Identity Problem

    Quote Originally Posted by alexmahone View Post
    sin\ 2u=\frac{2tan\ u}{1+tan^2\ u}
    Do you think you could show how you reached this answer? Thanks
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  7. #7
    MHF Contributor alexmahone's Avatar
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    Re: Trig Identity Problem

    Quote Originally Posted by bseymore View Post
    Do you think you could show how you reached this answer? Thanks
    Work backwards.

    \frac{2tan\ u}{1+tan^2\ u}=\frac{2tan\ u}{sec^2\ u}

    =2tan\ u\ cos^2\ u

    =2sin\ u\ cos\ u

    =sin\ 2u
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