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Math Help - if sin theta....

  1. #1
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    if sin theta....

    If sin theta = -3/5 and pi <theta <3pi/2, then tan theta = ?

    Can someone please show me how to work this? The only thing I know about this is:
    SOH, CAH, TOA
    That's really it. I dont know what theta is or how to solve this. it's an ACT problem in one of these practice tests.
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  2. #2
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    Find \cos\theta=\pm\sqrt{1-\sin^2\theta}.
    Then use this to compute \tan\theta.
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  3. #3
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    Quote Originally Posted by vemrygh View Post
    Find \cos\theta=\pm\sqrt{1-\sin^2\theta}.
    Then use this to compute \tan\theta.
    so then \cos\theta=\pm\sqrt{1-\-3/5^2\theta}.
    cos theta = sqrt[1-(9/25)]
    cos theta = sqrt(16/25) ??
    cos theta = -4/5
    am i on the right track?
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  4. #4
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    Yeah. It is correct of you to choose the negative solution of cosine instead of the positive since cosine is negative in the 3.quadrant.
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