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Thread: Can anyone help me with this problem?

  1. November 10th 2012, 10:57 AM #1
    derek1008
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    Can anyone help me with this problem?

    If sin(x)=-4/5 and (x) is in Quadrant III, find tan(x/2)
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  2. November 10th 2012, 11:39 AM #2
    skeeter
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    Re: Can anyone help me with this problem?

    Quote Originally Posted by derek1008 View Post
    If sin(x)=-4/5 and (x) is in Quadrant III, find tan(x/2)
    if x is a quad III angle ...

    (1) by sketching a reference triangle in quad III, you can calculate the value of \cos{x}.

    (2) \pi < x < \frac{3\pi}{2} \implies \frac{\pi}{2} < \frac{x}{2} < \frac{3\pi}{4}

    ... which says \frac{x}{2} is a quad II angle. Therefore, \tan\left(\frac{x}{2}\right) < 0.


    now use your half angle identity for tangent.
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