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Math Help - Got 3 questions

  1. #1
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    Got 3 questions

    i got 3 tough trigonometry questions for you all. Hope you help me solve them out. If necessary i can show you the steps i tried out myself but for
    the present i am limiting myself to the questions itself. any help would be highly appreciated and thanks in advance. the questions are with the attachment:
    Attached Thumbnails Attached Thumbnails Got 3 questions-3-trigo-questions.bmp  
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  2. #2
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    Quote Originally Posted by Pulock2009 View Post
    i got 3 tough trigonometry questions for you all. Hope you help me solve them out. If necessary i can show you the steps i tried out myself but for
    the present i am limiting myself to the questions itself. any help would be highly appreciated and thanks in advance. the questions are with the attachment:
    Please show the work you have done.
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  3. #3
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    2cos2x - 2cosx + 1 = 0
    4(cosx)^2 - 2 - 2cosx + 1 = 0
    4(cosx)^2 - 2cosx - 1 = 0

    cosx = -b +/- ......... quadratic forumla

    Solving it, we get
    cosx = (1 + root5)/4 or cosx = (1 - root5)/4
    Therefore, x=36 degrees or x=144 degrees

    And I suppose in the last one a, b and c add up to 180?
    Last edited by mr fantastic; June 7th 2010 at 04:29 AM.
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  4. #4
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    question

    Quote Originally Posted by darknight View Post
    2cos2x - 2cosx + 1 = 0
    4(cosx)^2 - 2 - 2cosx + 1 = 0
    4(cosx)^2 - 2cosx - 1 = 0

    cosx = -b +/- ......... quadratic forumla

    Solving it, we get
    cosx = (1 + root5)/4 or cosx = (1 - root5)/4
    Therefore, x=36 degrees or x=144 degrees

    And I suppose in the last one a, b and c add up to 180?
    i had worked upto the quadratic formulae but after getting the expression how does one knows that it 36 degrees and 144 degrees?also, my work for the second question is in the attachment.
    Last edited by Pulock2009; June 8th 2010 at 08:59 PM.
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  5. #5
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    Quote Originally Posted by Pulock2009 View Post
    i had worked upto the quadratic formulae but after getting the expression how does one knows that it 36 degrees and 144 degrees?also, my work for the second question is in the attachment.
    The moment I read the reply you got, I've been waiting to see if you asked that. You are probably not expected to know those exact values. Have you asked your instructor if you do?

    The derivation of them is not straightforward (but someone will do it if you really really want to know).
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