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Math Help - Finding exact values in quadrants,.

  1. #1
    Junior Member
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    Finding exact values in quadrants,.

    If i have a question saying find the exact value of cos 2 theta given that sin theta = - 3/5 and theta is in quadrant III.
    answear is 7/25 but I don't know how to get there explain and I will give you a huge THANKS!
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  2. #2
    MHF Contributor red_dog's Avatar
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    \cos 2\theta =1-2\sin^2\theta

    Then replace \sin\theta with -\frac{3}{5}
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