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Math Help - basic trigonometry problems, help?

  1. #1
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    Exclamation basic trigonometry problems, help?

    given cos θ = 3/5, tan θ < 0
    find:
    sin 2θ
    cos 2θ
    cot 2θ

    use half measure identities to find exact values of the following:

    tan 15 degrees
    sec π/12


    THANK YOU SO MUCH!
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  2. #2
    MHF Contributor
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    Quote Originally Posted by pongpong View Post
    given cos θ = 3/5, tan θ < 0
    find:
    sin 2θ
    cos 2θ
    cot 2θ

    use half measure identities to find exact values of the following:

    tan 15 degrees
    sec π/12


    THANK YOU SO MUCH!

    Since cos is positive and tan is negative , so the angle will be in quadrant 4 . Draw a triangle in quadrant 4 and find sin and tan .
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  3. #3
    MHF Contributor
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    West Malaysia
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    Quote Originally Posted by pongpong View Post
    use half measure identities to find exact values of the following:

    tan 15 degrees
    tan 15 = tan 1/2(30)

    You can use this identity .

     <br />
\tan\frac{\theta}{2}=\pm\sqrt{\frac{1-cos\theta}{1+cos\theta}}<br />

    where \theta is 30 .

    In this case , \theta is in the first quadrant so it will be positive .
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