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Math Help - [SOLVED] Trignometry and Radians

  1. #1
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    Cool [SOLVED] Trignometry and Radians

    Here's the question



    I have solved the first part and got the following equation, which is correct:


    y=(6sin2x)+3

    Now for part (ii) I have solved till

    sin2x=\frac{-1}{2}

    And don't know how to get the correct answer:

    Spoiler:
    x =7pi/12 or 1.83 rad


    Thanks in advance!
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  2. #2
    MHF Contributor
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    Quote Originally Posted by unstopabl3 View Post
    Here's the question



    I have solved the first part and got the following equation, which is correct:


    y=(6sin2x)+3

    Now for part (ii) I have solved till

    sin2x=\frac{-1}{2}

    And don't know how to get the correct answer:

    Spoiler:
    x =7pi/12 or 1.83 rad


    Thanks in advance!
    Hi unstopabl3,

    sin(2x)=-\frac{1}{2}

    the first time this occurs is in the 3rd quadrant,
    as sin(angle) points out the y co-ordinate of a point on the circle.

    Hence the angle 2x is

    {\pi}+sin^{-1}\left(\frac{1}{2}\right)

    ={\pi}+\frac{{\pi}}{6}=\frac{7{\pi}}{6}

    x is half that.
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  3. #3
    Member
    Joined
    Sep 2009
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    148
    Yea, I figured it out myself as well! Haha

    Thanks for the quick and easy to understand reply!
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